I don't really know what all is going on here beyond that. Maybe you could figure it out?
crash-2021-10-31_14.26.55-fml.txt

to be clear I just had this crash too, and it is entirely random

java.lang.NullPointerException
at com.github.lehjr.numina.util.client.event.ArmorLayerSetup.addCustomArmorLayer(ArmorLayerSetup.java:70)
at com.github.lehjr.numina.util.client.event.ArmorLayerSetup.loadComplete(ArmorLayerSetup.java:62)
at com.github.lehjr.numina.basemod.Numina$MyStaticClientOnlyEventHandler.loadComplete(Numina.java:142)
at net.minecraftforge.eventbus.ASMEventHandler_444_MyStaticClientOnlyEventHandler_loadComplete_FMLLoadCompleteEvent.invoke(.dynamic)

looks like a thread collision that sometimes occur if one registry thread is ahead of the other as loadComplete might get fired too soon.