This error only happens when betterfoliage is enabled. i didn´t find a workaround so i´m reporting it in hopes it can be fixed.
The game crashes upon defeating the 1000HP version of the vein floater with the attached log:

crash-2020-12-30_01.40.39-client.txt

This is on More-Planets-1.12.2-2.2.0-GC281 and BetterFoliage-MC1.12-2.3.1