Unknownreported this bug
I found a really interesting bug, if a mob is in the spawn region that is loaded by paper permanent then the mob will be corrupted after restart. This happens in Model Engine 4.0.3 and Mythicmobs 5.4.1. The mob with the model was also persistent so it cannot despawn after restart.
[Legacy attachment omitted] Here is a screenshot how the model looks like after restart, when it was in a spawn chunk.
Paper got the following options in their world config: keep-spawn-loaded: true keep-spawn-loaded-range: 3
With these config options you can test yourself this bug.