Using Regeneration-1.12.2-1.5.6 and finding that it crashes occasionally from this same issue.
crash-2019-03-25_16.09.09-client.txt

Downgraded to version 1.5.5 and am having the same issue. The only cause of this crash I can think of is that I changed the config.
This part in particular: B:changeMySkin=false
Also, I have the skin folder empty (I deleted the contents)

Interesting, I'll take another look at this tonight

So I'm playing with this on a server and the issue seems to be that when two players see each other the game crashes. Works perfectly fine until they render another player. Have tried a new world/player data which doesn't solve the issue. Not sure how to resolve this issue.

https://minecraft.curseforge.com/projects/regeneration/files/2691684