I am getting crashes in the log below that are related to Frost Rebuke enchantment. I am pretty sure that null is being passed or is result of calls called by mob grinding utils as I used a different fake player to kill mobs before in the pack and haven't had this issue.

https://pastebin.com/8GVhjrEs

Version: mob_grinding_utils-1.16.5-0.4.2

Also getting this issue. This is likely related to MinecraftForge/MinecraftForge#6358

Should be fixed in ebc03ca