Using the latest versions of Citadel and Ice and Fire create this spam in the log

[Render thread/FATAL] [net.minecraft.util.concurrent.ThreadTaskExecutor/]: Error executing task on Client
java.lang.NullPointerException: Cannot invoke "java.lang.ref.WeakReference.get()" because "this.entity" is null
at com.github.alexthe666.citadel.server.entity.datatracker.EntityProperties.getEntity(EntityProperties.java:63) ~[citadel:1.7.2-1.16.5]
at com.github.alexthe666.iceandfire.entity.props.ChainEntityProperties.loadNBTData(ChainEntityProperties.java:54) ~[iceandfire:2.1.8-1.16.5]
at com.github.alexthe666.citadel.server.entity.datatracker.EntityProperties.loadTrackingSensitiveData(EntityProperties.java:112) ~[citadel:1.7.2-1.16.5]
at com.github.alexthe666.citadel.ClientProxy.handlePropertiesPacket(ClientProxy.java:126) ~[citadel:1.7.2-1.16.5]
at com.github.alexthe666.citadel.server.message.PropertiesMessage$Handler.lambda$handle$0(PropertiesMessage.java:50) ~[citadel:1.7.2-1.16.5]
at net.minecraftforge.fml.network.NetworkEvent$Context.enqueueWork(NetworkEvent.java:215) ~[forge:?]
at com.github.alexthe666.citadel.server.message.PropertiesMessage$Handler.handle(PropertiesMessage.java:48) ~[citadel:1.7.2-1.16.5]
at net.minecraftforge.fml.network.simple.IndexedMessageCodec.lambda$tryDecode$3(IndexedMessageCodec.java:128) ~[forge:?]
at java.util.Optional.ifPresent(Unknown Source) ~[?:?]
at net.minecraftforge.fml.network.simple.IndexedMessageCodec.tryDecode(IndexedMessageCodec.java:128) ~[forge:?]
at net.minecraftforge.fml.network.simple.IndexedMessageCodec.consume(IndexedMessageCodec.java:162) ~[forge:?]
at net.minecraftforge.fml.network.simple.SimpleChannel.networkEventListener(SimpleChannel.java:80) ~[forge:?]
at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247) ~[eventbus-4.0.0.jar:?]
at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239) ~[eventbus-4.0.0.jar:?]
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302) ~[eventbus-4.0.0.jar:?]
at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-4.0.0.jar:?]
at net.minecraftforge.fml.network.NetworkInstance.dispatch(NetworkInstance.java:86) ~[forge:?]
at net.minecraftforge.fml.network.NetworkHooks.lambda$onCustomPayload$1(NetworkHooks.java:91) ~[forge:?]
at java.util.Optional.map(Unknown Source) ~[?:?]
at net.minecraftforge.fml.network.NetworkHooks.onCustomPayload(NetworkHooks.java:91) ~[forge:?]
at net.minecraft.client.network.play.ClientPlayNetHandler.func_147240_a(ClientPlayNetHandler.java:1904) ~[?:?]
at net.minecraft.network.play.server.SCustomPayloadPlayPacket.func_148833_a(SCustomPayloadPlayPacket.java:59) ~[?:?]
at net.minecraft.network.play.server.SCustomPayloadPlayPacket.func_148833_a(SCustomPayloadPlayPacket.java:11) ~[?:?]
at net.minecraft.network.PacketThreadUtil.lambda$checkThreadAndEnqueue$0(PacketThreadUtil.java:36) ~[?:?]
at net.optifine.util.PacketRunnable.run(PacketRunnable.java:28) ~[?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(ThreadTaskExecutor.java:189) ~[?:?]
at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) ~[?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(ThreadTaskExecutor.java:151) ~[?:?]
at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213160_bf(ThreadTaskExecutor.java:128) ~[?:?]
at net.minecraft.client.Minecraft.func_195542_b(Minecraft.java:947) ~[?:?]
at net.minecraft.client.Minecraft.func_99999_d(Minecraft.java:607) ~[?:?]
at net.minecraft.client.main.Main.main(Main.java:184) ~[minecraft-1.16.5-client.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:?]
at java.lang.reflect.Method.invoke(Unknown Source) ~[?:?]
at net.minecraftforge.fml.loading.FMLClientLaunchProvider.lambda$launchService$0(FMLClientLaunchProvider.java:51) ~[forge-1.16.5-36.1.32-launcher.jar:36.1]
at cpw.mods.modlauncher.LaunchServiceHandlerDecorator.launch(LaunchServiceHandlerDecorator.java:37) [modlauncher-8.0.9.jar:?]
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:54) [modlauncher-8.0.9.jar:?]
at cpw.mods.modlauncher.LaunchServiceHandler.launch(LaunchServiceHandler.java:72) [modlauncher-8.0.9.jar:?]
at cpw.mods.modlauncher.Launcher.run(Launcher.java:82) [modlauncher-8.0.9.jar:?]
at cpw.mods.modlauncher.Launcher.main(Launcher.java:66) [modlauncher-8.0.9.jar:?]
at io.github.zekerzhayard.forgewrapper.installer.Main.main(Main.java:50) [ForgeWrapper-1.4.2.jar:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[?:?]
at jdk.internal.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) ~[?:?]
at jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) ~[?:?]
at java.lang.reflect.Method.invoke(Unknown Source) ~[?:?]
at org.multimc.onesix.OneSixLauncher.launchWithMainClass(OneSixLauncher.java:196) [NewLaunch.jar:?]
at org.multimc.onesix.OneSixLauncher.launch(OneSixLauncher.java:231) [NewLaunch.jar:?]
at org.multimc.EntryPoint.listen(EntryPoint.java:143) [NewLaunch.jar:?]
at org.multimc.EntryPoint.main(EntryPoint.java:34) [NewLaunch.jar:?]

What Citadel Version are you using?

1.7.2

1.7.2

Downgrade to 1.7.0 or 1.7.1 and should be solved.

Same problem and for me it resulted in a crash when I got attacked by a dragon

Just for updated info on this, I started getting this after a random troll spawned and then turned to stone.

Downgrading is not a solution, that is a workaround. What we need is some feedback on what the cause is and what possible resolutions exist. As mods which require Citadel update you will no longer be able to use this workaround.
The cause of this issue is specifically when a mob from one of the developer's mods needs to be rendered. If you are in a dimension where these mobs do not spawn you will not experience the issue. This has been going on for the last 3 releases of Citadel without being resolved, so some kind of feedback would be nice.