Minecraft Version: 1.16.5
Shulkers structure system version: 0.1
Forge version: 36.1.24

I've noticed that when I was testing this mod with my modpack beforehand it was throwing a bunch of errors in the log whenever generating a custom structure. The lines in the log are seen here:
[16:56:55] [Server thread/ERROR]: Exception loading structure piece with id minecraft:simplestructure
net.minecraft.util.ResourceLocationException: Non [a-z0-9_.-] character in namespace of location: C:\Users\Nathan Lamb\Documents\curseforge\minecraft\Instances\Survival of the Fittest\shulkerssupersimplestructuresystem\structureNBTs\fallen_oak_log01.nbt
at net.minecraft.util.ResourceLocation.(ResourceLocation.java:31) ~[?:?]
at net.minecraft.util.ResourceLocation.(ResourceLocation.java:38) ~[?:?]
at com.nhwhite3118.structures.simplestructure.SimpleStructurePieces$Piece.(SimpleStructurePieces.java:97) ~[shulkerssupersimplestructuresystem:0.1]
at com.nhwhite3118.structures.Structures$$Lambda$14152/0x0000000000000000.load(Unknown Source) ~[?:?]
at net.minecraft.world.gen.feature.structure.Structure.func_236393_a_(Structure.java:119) [?:?]
at net.minecraft.world.chunk.storage.ChunkSerializer.func_235967_a_(ChunkSerializer.java:438) [?:?]
at net.minecraft.world.chunk.storage.ChunkSerializer.func_222656_a(ChunkSerializer.java:170) [?:?]
at net.minecraft.world.server.ChunkManager.func_223170_j(ChunkManager.java:480) [?:?]
at net.minecraft.world.server.ChunkManager$$Lambda$16567/0x0000000000000000.get(Unknown Source) [?:?]
at java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1604) [?:1.8.0_292]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144) [?:?]
at net.minecraft.world.server.ServerChunkProvider$ChunkExecutor.func_213166_h(ServerChunkProvider.java:514) [?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118) [?:?]
at net.minecraft.world.server.ServerChunkProvider$ChunkExecutor.func_213168_p(ServerChunkProvider.java:522) [?:?]
at net.minecraft.world.server.ServerChunkProvider.func_217234_d(ServerChunkProvider.java:267) [?:?]
at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:722) [?:?]
at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:711) [?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213161_c(SourceFile:127) [?:?]
at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:697) [?:?]
at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:646) [?:?]
at net.minecraft.server.MinecraftServer.func_240783_a_(MinecraftServer.java:232) [?:?]
at net.minecraft.server.MinecraftServer$$Lambda$16396/0x0000000000000000.run(Unknown Source) [?:?]
at java.lang.Thread.run(Thread.java:823) [?:1.8.0_292]

This doesn't happen without any other mod so it definitely seems to be some other mod that is causing this error to appear. If it helps there are two mods that are often mentioned in these errors which are Supplementaries and Lava Monsters.

The full log can be found here: https://gist.github.com/NJL5390/405183b20d42ed17b29841bbb78d58cf