The following error seems to cause severe tps issues to the point of unplayability.
Lags were due to another mod. These errors still show up tho.

Mod version: mowziesmobs-1.5.16
MC version: 1.16.4
Forge: forge-1.16.4-35.1.37
Modpack: Mineshafts & Monsters v1.2.2

[19Apr2021 17:35:58.560] [Server thread/FATAL] [net.minecraft.util.concurrent.ThreadTaskExecutor/]: Error executing task on Server java.lang.NullPointerException: null at com.bobmowzie.mowziesmobs.server.message.mouse.MessageRightMouseUp$Handler.accept(MessageRightMouseUp.java:40) ~[mowziesmobs:1.5.16] at com.bobmowzie.mowziesmobs.server.message.mouse.MessageRightMouseUp$Handler.lambda$accept$0(MessageRightMouseUp.java:33) ~[mowziesmobs:1.5.16] at net.minecraftforge.fml.network.NetworkEvent$Context.enqueueWork(NetworkEvent.java:215) ~[forge:?] at com.bobmowzie.mowziesmobs.server.message.mouse.MessageRightMouseUp$Handler.accept(MessageRightMouseUp.java:33) ~[mowziesmobs:1.5.16] at com.bobmowzie.mowziesmobs.server.message.mouse.MessageRightMouseUp$Handler.accept(MessageRightMouseUp.java:28) ~[mowziesmobs:1.5.16] at net.minecraftforge.fml.network.simple.IndexedMessageCodec.lambda$tryDecode$3(IndexedMessageCodec.java:128) ~[forge:?] at java.util.Optional.ifPresent(Unknown Source) ~[?:1.8.0_281] at net.minecraftforge.fml.network.simple.IndexedMessageCodec.tryDecode(IndexedMessageCodec.java:128) ~[forge:?] at net.minecraftforge.fml.network.simple.IndexedMessageCodec.consume(IndexedMessageCodec.java:162) ~[forge:?] at net.minecraftforge.fml.network.simple.SimpleChannel.networkEventListener(SimpleChannel.java:80) ~[forge:?] at net.minecraftforge.eventbus.EventBus.doCastFilter(EventBus.java:247) ~[eventbus-4.0.0.jar:?] at net.minecraftforge.eventbus.EventBus.lambda$addListener$11(EventBus.java:239) ~[eventbus-4.0.0.jar:?] at net.minecraftforge.eventbus.EventBus.post(EventBus.java:302) ~[eventbus-4.0.0.jar:?] at net.minecraftforge.eventbus.EventBus.post(EventBus.java:283) ~[eventbus-4.0.0.jar:?] at net.minecraftforge.fml.network.NetworkInstance.dispatch(NetworkInstance.java:84) ~[forge:?] at net.minecraftforge.fml.network.NetworkHooks.lambda$onCustomPayload$1(NetworkHooks.java:88) ~[forge:?] at java.util.Optional.map(Unknown Source) ~[?:1.8.0_281] at net.minecraftforge.fml.network.NetworkHooks.onCustomPayload(NetworkHooks.java:88) ~[forge:?] at net.minecraft.network.play.ServerPlayNetHandler.func_147349_a(ServerPlayNetHandler.java:1413) ~[?:?] at net.minecraft.network.play.client.CCustomPayloadPacket.func_148833_a(CCustomPayloadPacket.java:42) ~[?:?] at net.minecraft.network.play.client.CCustomPayloadPacket.func_148833_a(CCustomPayloadPacket.java:12) ~[?:?] at net.minecraft.network.PacketThreadUtil.func_225383_a(SourceFile:21) ~[?:?] at net.minecraft.util.concurrent.TickDelayedTask.run(SourceFile:18) ~[?:?] at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213166_h(SourceFile:144) ~[?:?] at net.minecraft.util.concurrent.RecursiveEventLoop.func_213166_h(SourceFile:23) ~[?:?] at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:733) ~[?:?] at net.minecraft.server.MinecraftServer.func_213166_h(MinecraftServer.java:159) ~[?:?] at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213168_p(SourceFile:118) ~[?:?] at net.minecraft.server.MinecraftServer.func_213205_aW(MinecraftServer.java:716) ~[?:?] at net.minecraft.server.MinecraftServer.func_213168_p(MinecraftServer.java:710) ~[?:?] at net.minecraft.util.concurrent.ThreadTaskExecutor.func_213161_c(SourceFile:127) ~[?:?] at net.minecraft.server.MinecraftServer.func_213202_o(MinecraftServer.java:696) ~[?:?] at net.minecraft.server.MinecraftServer.func_240802_v_(MinecraftServer.java:645) ~[?:?] at net.minecraft.server.MinecraftServer.lambda$startServer$0(MinecraftServer.java:232) ~[?:?] at java.lang.Thread.run(Unknown Source) [?:1.8.0_281]

Fixed