Steps to reproduce crash (found in DeceasedCraft 5.5.5)

1. Create a superflat world
2. Open the main menu
3. Crash

complete stacktrace:

---- Minecraft Crash Report ----
// You should try our sister game, Minceraft!

Time: 11/11/24, 12:21 AM
Description: Exception in server tick loop

java.lang.NoClassDefFoundError: mcjty/lostcities/varia/TodoQueue
at com.bawnorton.dcfixes.FasterLostCities.m_7176_(FasterLostCities.java:87) ~[DeceasedCraftFixes-1.0.7+1.18.2.jar%23122!/:?] {re:mixin,re:classloading}
at net.minecraft.world.level.saveddata.SavedData.m_77757_(SavedData.java:36) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,re:classloading,pl:mixin:APP:fastasyncworldsave.mixins.json:SavedDataMixin,pl:mixin:A}
at net.minecraft.world.level.storage.DimensionDataStorage.m_164865_(DimensionDataStorage.java:161) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
at java.util.HashMap.forEach(HashMap.java:1421) ~[?:?] {re:mixin}
at net.minecraft.world.level.storage.DimensionDataStorage.m_78151_(DimensionDataStorage.java:159) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,re:classloading,pl:accesstransformer:B}
at net.minecraft.server.level.ServerLevel.m_8806_(ServerLevel.java:717) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_tick,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_ispositionentityticking,xf:fml:sereneseasons:temperature_transformer,re:classloading,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_tick,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_ispositionentityticking,xf:fml:sereneseasons:temperature_transformer,pl:mixin:APP:modernfix-common.mixins.json:perf.cache_strongholds.ServerLevelMixin,pl:mixin:APP:modernfix-common.mixins.json:bugfix.chunk_deadlock.ServerLevelMixin,pl:mixin:APP:snowrealmagic.mixins.json:ServerLevelMixin,pl:mixin:APP:pluto.mixins.json:fast_entity_access.ServerLevelMixin,pl:mixin:APP:starlight.mixins.json:common.world.ServerWorldMixin,pl:mixin:APP:crafttweaker.mixins.json:common.transform.world.level.MixinServerLevel,pl:mixin:APP:physicsmod.mixins.json:fabricapi.MixinServerWorld,pl:mixin:APP:immersiveengineering.mixins.json:coremods.ServerWorldMixin,pl:mixin:APP:canary.mixins.json:alloc.chunk_random.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:chunk.replace_streams.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:entity.inactive_navigations.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:profiler.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:util.accessors.ServerLevelAccessor,pl:mixin:APP:canary.mixins.json:world.block_entity_ticking.sleeping.ServerLevelMixin,pl:mixin:APP:cold_sweat.mixin.json:MixinBlockUpdate,pl:mixin:APP:ritchiesprojectilelib.mixins.json:ServerLevelMixin,pl:mixin:APP:zombieawareness.mixins.json:MixinPlaySound,pl:mixin:APP:zombieawareness.mixins.json:MixinLevelEvent,pl:mixin:APP:alternate_current.mixins.json:ServerLevelMixin,pl:mixin:APP:enhancedcelestials.mixins.json:MixinServerWorld,pl:mixin:APP:assets/sound_physics_remastered/sound_physics_remastered.mixins.json:ServerWorldMixin,pl:mixin:APP:create.mixins.json:accessor.ServerLevelAccessor,pl:mixin:A}
at net.minecraft.server.level.ServerLevel.m_8643_(ServerLevel.java:696) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_tick,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_ispositionentityticking,xf:fml:sereneseasons:temperature_transformer,re:classloading,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_tick,xf:fml:openpartiesandclaims:xaero_pac_serverlevel_ispositionentityticking,xf:fml:sereneseasons:temperature_transformer,pl:mixin:APP:modernfix-common.mixins.json:perf.cache_strongholds.ServerLevelMixin,pl:mixin:APP:modernfix-common.mixins.json:bugfix.chunk_deadlock.ServerLevelMixin,pl:mixin:APP:snowrealmagic.mixins.json:ServerLevelMixin,pl:mixin:APP:pluto.mixins.json:fast_entity_access.ServerLevelMixin,pl:mixin:APP:starlight.mixins.json:common.world.ServerWorldMixin,pl:mixin:APP:crafttweaker.mixins.json:common.transform.world.level.MixinServerLevel,pl:mixin:APP:physicsmod.mixins.json:fabricapi.MixinServerWorld,pl:mixin:APP:immersiveengineering.mixins.json:coremods.ServerWorldMixin,pl:mixin:APP:canary.mixins.json:alloc.chunk_random.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:chunk.replace_streams.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:entity.inactive_navigations.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:profiler.ServerLevelMixin,pl:mixin:APP:canary.mixins.json:util.accessors.ServerLevelAccessor,pl:mixin:APP:canary.mixins.json:world.block_entity_ticking.sleeping.ServerLevelMixin,pl:mixin:APP:cold_sweat.mixin.json:MixinBlockUpdate,pl:mixin:APP:ritchiesprojectilelib.mixins.json:ServerLevelMixin,pl:mixin:APP:zombieawareness.mixins.json:MixinPlaySound,pl:mixin:APP:zombieawareness.mixins.json:MixinLevelEvent,pl:mixin:APP:alternate_current.mixins.json:ServerLevelMixin,pl:mixin:APP:enhancedcelestials.mixins.json:MixinServerWorld,pl:mixin:APP:assets/sound_physics_remastered/sound_physics_remastered.mixins.json:ServerWorldMixin,pl:mixin:APP:create.mixins.json:accessor.ServerLevelAccessor,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_129885_(MinecraftServer.java:538) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,re:classloading,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_195514_(MinecraftServer.java:563) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,re:classloading,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,pl:mixin:A}
at net.minecraft.client.server.IntegratedServer.m_5705_(IntegratedServer.java:76) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,xf:fml:openpartiesandclaims:xaero_pac_integratedserver_tickpaused,pl:runtimedistcleaner:A,re:classloading,xf:fml:openpartiesandclaims:xaero_pac_integratedserver_tickpaused,pl:mixin:A,pl:runtimedistcleaner:A}
at net.minecraft.server.MinecraftServer.m_130011_(MinecraftServer.java:685) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,re:classloading,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,pl:mixin:A}
at net.minecraft.server.MinecraftServer.m_177918_(MinecraftServer.java:261) ~[client-1.18.2-20220404.173914-srg.jar%23281!/:?] {re:mixin,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,re:classloading,pl:accesstransformer:B,xf:fml:openpartiesandclaims:xaero_pac_minecraftserverclass,xf:fml:xaeroworldmap:xaero_wm_minecraftserver,xf:fml:xaerominimapfair:xaero_minecraftserver,pl:mixin:A}
at java.lang.Thread.run(Thread.java:833) ~[?:?] {re:mixin}
Caused by: java.lang.ClassNotFoundException: mcjty.lostcities.varia.TodoQueue
at cpw.mods.cl.ModuleClassLoader.loadClass(ModuleClassLoader.java:141) ~[securejarhandler-1.0.8.jar:?] {}
at java.lang.ClassLoader.loadClass(ClassLoader.java:520) ~[?:?] {}
... 13 more

yes, superflat is not supported