For some weird reason if paired with Truly Modular JER causes truly modulars reload to fail, but only if the player connects directly to the server. this is probably related to #392 , in the logs the following shows up:
[20:32:50] [Render thread/ERROR]: Failed to list path /data java.nio.file.NotDirectoryException: /data at jdk.nio.zipfs.ZipDirectoryStream.<init>(ZipDirectoryStream.java:58) ~[jdk.zipfs:?] at jdk.nio.zipfs.ZipPath.newDirectoryStream(ZipPath.java:755) ~[jdk.zipfs:?] at jdk.nio.zipfs.ZipFileSystemProvider.newDirectoryStream(ZipFileSystemProvider.java:262) ~[jdk.zipfs:?] at java.nio.file.Files.newDirectoryStream(Files.java:482) ~[?:?] at net.minecraft.class_3259.method_14406(class_3259.java:130) ~[client-intermediary.jar:?] at net.minecraft.class_6861.<init>(class_6861.java:35) ~[client-intermediary.jar:?] at net.minecraft.class_3304.method_18232(class_3304.java:46) ~[client-intermediary.jar:?] at jeresources.util.LootTableHelper.getLootDataManager(LootTableHelper.java:182) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at jeresources.util.LootTableHelper.toDrops(LootTableHelper.java:95) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at jeresources.util.PlantHelper.getSeeds(PlantHelper.java:14) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at jeresources.entry.PlantEntry.registerGrass(PlantEntry.java:28) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at jeresources.registry.PlantRegistry.<init>(PlantRegistry.java:25) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at jeresources.registry.PlantRegistry.getInstance(PlantRegistry.java:19) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at jeresources.proxy.CommonProxy.initCompatibility(CommonProxy.java:11) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at jeresources.jei.JEIConfig.registerCategories(JEIConfig.java:98) ~[JustEnoughResources-Fabric-1.20.1-1.4.0.238.jar:?] at mezz.jei.library.load.PluginLoader.lambda$createRecipeCategories$3(PluginLoader.java:90) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at mezz.jei.library.load.PluginCaller.callOnPlugins(PluginCaller.java:27) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at mezz.jei.library.load.PluginLoader.createRecipeCategories(PluginLoader.java:90) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at mezz.jei.library.load.PluginLoader.createRecipeManager(PluginLoader.java:119) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at mezz.jei.library.startup.JeiStarter.start(JeiStarter.java:132) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at mezz.jei.fabric.startup.ClientLifecycleHandler.startJei(ClientLifecycleHandler.java:84) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at mezz.jei.fabric.startup.ClientLifecycleHandler.lambda$registerEvents$1(ClientLifecycleHandler.java:53) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at mezz.jei.fabric.events.JeiLifecycleEvents.lambda$static$4(JeiLifecycleEvents.java:28) ~[jei-1.20.1-fabric-15.2.0.27.jar:?] at net.minecraft.class_634.handler$bbh001$jei$handleUpdateRecipes(class_634.java:6222) ~[client-intermediary.jar:?] at net.minecraft.class_634.method_11106(class_634.java:1445) ~[client-intermediary.jar:?] at net.minecraft.class_2788.method_11997(class_2788.java:32) ~[client-intermediary.jar:?] at net.minecraft.class_2788.method_11054(class_2788.java:14) ~[client-intermediary.jar:?] at net.minecraft.class_2600.method_11072(class_2600.java:22) ~[client-intermediary.jar:?] at net.minecraft.class_1255.method_18859(class_1255.java:156) ~[client-intermediary.jar:?] at net.minecraft.class_4093.method_18859(class_4093.java:23) ~[client-intermediary.jar:?] at net.minecraft.class_1255.method_16075(class_1255.java:130) ~[client-intermediary.jar:?] at net.minecraft.class_1255.method_5383(class_1255.java:115) ~[client-intermediary.jar:?] at net.minecraft.class_310.method_1523(class_310.java:1175) ~[client-intermediary.jar:?] at net.minecraft.class_310.method_1514(class_310.java:802) ~[client-intermediary.jar:?] at net.minecraft.client.main.Main.main(Main.java:250) ~[1.20.1-0.14.22.jar:?] at net.fabricmc.loader.impl.game.minecraft.MinecraftGameProvider.launch(MinecraftGameProvider.java:468) ~[fabric-loader-0.14.22.jar:?] at net.fabricmc.loader.impl.launch.knot.Knot.launch(Knot.java:74) ~[fabric-loader-0.14.22.jar:?] at net.fabricmc.loader.impl.launch.knot.KnotClient.main(KnotClient.java:23) ~[fabric-loader-0.14.22.jar:?]

this gets logged a lot during connect on the client and the stacktrace does not mention any class related to truly modular, and if the client first joins singleplayer its also fine so it seems the issue comes from JER not building its resources correctly, crashing out some things truly modular requires for a successfull reload.