Everything works as intended with beta1, but updating to beta2 broke something. Guessing it's a compatibility issue with modded biomes and the fallen trees? Couldn't get a crash report, but it did output a 45.56mb latest.log file. Most of it looked like the following:

[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: java.lang.NullPointerException
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList.func_234004_a_(SourceFile:42)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList$$Lambda$11486/329232102.accept(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at java.util.ArrayList.forEach(ArrayList.java:1249)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList.func_226314_a_(SourceFile:42)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList.func_226318_b_(SourceFile:521)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.world.gen.blockstateprovider.WeightedBlockStateProvider.func_225574_a_(SourceFile:42)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at projectvibrantjourneys.init.PVJWorldGen.addFallenTreeFeatures(PVJWorldGen.java:130)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.eventbus.ASMEventHandler_286_PVJWorldGen_addFallenTreeFeatures_BiomeLoadingEvent.invoke(.dynamic)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.eventbus.ASMEventHandler.invoke(ASMEventHandler.java:85)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.eventbus.EventBus$$Lambda$2562/1703034311.invoke(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.common.ForgeHooks.enhanceBiome(ForgeHooks.java:944)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.world.biome.Biome.lambda$null$8(Biome.java:75)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.world.biome.Biome$$Lambda$2146/265672341.apply(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.datafixers.util.Function8.lambda$null$6(Function8.java:22)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.datafixers.util.Function8$$Lambda$11267/316623218.apply(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.datafixers.util.Function4.lambda$null$2(Function4.java:14)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.datafixers.util.Function4$$Lambda$11266/323123609.apply(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.DataResult$Instance.ap2(DataResult.java:315)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.datafixers.kinds.Applicative.ap4(Applicative.java:84)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.codecs.RecordCodecBuilder$Instance$7.decode(RecordCodecBuilder.java:404)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.codecs.RecordCodecBuilder$2.decode(RecordCodecBuilder.java:107)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.MapDecoder.lambda$compressedDecode$0(MapDecoder.java:52)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.MapDecoder$$Lambda$11153/1954922915.apply(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.DataResult.lambda$flatMap$10(DataResult.java:138)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.DataResult$$Lambda$1193/1639066642.apply(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.DataResult.flatMap(DataResult.java:136)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.MapDecoder.compressedDecode(MapDecoder.java:52)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.MapCodec$MapCodecCodec.decode(MapCodec.java:91)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.Decoder.parse(Decoder.java:18)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.WorldSettingsImport$IResourceAccess$RegistryAccess.func_241879_a(WorldSettingsImport.java:236)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.WorldSettingsImport.func_241805_a_(WorldSettingsImport.java:131)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.WorldSettingsImport.func_240885_a_(WorldSettingsImport.java:105)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.WorldSettingsImport$$Lambda$11255/585964670.apply(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.DataResult.lambda$flatMap$10(DataResult.java:138)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.DataResult$$Lambda$1193/1639066642.apply(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.datafixers.util.Either$Left.map(Either.java:38)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.serialization.DataResult.flatMap(DataResult.java:136)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.WorldSettingsImport.func_241797_a_(WorldSettingsImport.java:104)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.DynamicRegistries.func_243610_a(DynamicRegistries.java:144)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.DynamicRegistries.func_243608_a(DynamicRegistries.java:132)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.WorldSettingsImport.func_244336_a(WorldSettingsImport.java:53)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.registry.DynamicRegistries.func_239770_b_(DynamicRegistries.java:85)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.screen.CreateWorldScreen.func_243425_a(CreateWorldScreen.java:112)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.screen.WorldSelectionScreen.func_214326_e(SourceFile:54)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.screen.WorldSelectionScreen$$Lambda$11183/691740926.onPress(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.widget.button.Button.func_230930_b_(SourceFile:33)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.widget.button.AbstractButton.func_230982_a_(SourceFile:16)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.widget.Widget.func_231044_a_(Widget.java:136)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.INestedGuiEventHandler.func_231044_a_(SourceFile:27)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MouseHelper.func_198033_b(MouseHelper.java:87)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MouseHelper$$Lambda$11143/1185666309.run(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.gui.screen.Screen.func_231153_a_(Screen.java:427)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MouseHelper.func_198023_a(MouseHelper.java:85)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MouseHelper.func_228030_c_(MouseHelper.java:175)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MouseHelper$$Lambda$11142/1265749190.run(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.concurrent.ThreadTaskExecutor.execute(ThreadTaskExecutor.java:106)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MouseHelper.func_228028_b_(MouseHelper.java:174)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MouseHelper$$Lambda$9515/1147314184.invoke(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at org.lwjgl.glfw.GLFWMouseButtonCallbackI.callback(GLFWMouseButtonCallbackI.java:36)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at org.lwjgl.system.JNI.invokeV(Native Method)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at org.lwjgl.glfw.GLFW.glfwPollEvents(GLFW.java:3101)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at com.mojang.blaze3d.systems.RenderSystem.flipFrame(SourceFile:102)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.MainWindow.func_227802_e_(MainWindow.java:398)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.Minecraft.func_195542_b(Minecraft.java:996)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:607)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.client.main.Main.main(Main.java:184)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at java.lang.reflect.Method.invoke(Method.java:497)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:51)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.fml.loading.FMLClientLaunchProvider$$Lambda$483/668929853.call(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at cpw.mods.modlauncher.Launcher.run(Launcher.java:82)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at cpw.mods.modlauncher.Launcher.main(Launcher.java:66)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: java.lang.NullPointerException
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList.func_234004_a_(SourceFile:42)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList$$Lambda$11486/329232102.accept(Unknown Source)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at java.util.ArrayList.forEach(ArrayList.java:1249)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList.func_226314_a_(SourceFile:42)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.util.WeightedList.func_226318_b_(SourceFile:521)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraft.world.gen.blockstateprovider.WeightedBlockStateProvider.func_225574_a_(SourceFile:42)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at projectvibrantjourneys.init.PVJWorldGen.addFallenTreeFeatures(PVJWorldGen.java:130)
[17:35:02] [Render thread/INFO]: [net.minecraft.util.WeightedList:func_226318_b_:525]: at net.minecraftforge.eventbus.ASMEventHandler_286_PVJWorldGen_addFallenTreeFeatures_BiomeLoadingEvent.invoke(.dynamic)

From what I can tell it's because I assumed modded trees would use the same block state provider so I passed null for a parameter. I'll put up a beta3 version on curseforge with a fix that hopefully should work.

It did. Worlds are loading fine with beta3. Explored some new chunks and everything seems to be generating properly from what I can tell. However, the log after seems to have some answers thanks to Blame.
latest.log

I've rewritten the way the fallen trees are registered which hopefully should help with mod compatibility. I've uploaded a 4th beta version to CurseForge.

Working as intended, and a clean log to boot. :)