Crash that happens when a Magma Cube is picked up with an Edelwood Bucket, not corrently known if restricted to Valhelsia 3.1.8a or the mod alone - one of the Valhelsia devs recommended I open an issue about it.
Game log:
2021-02-15-1.log

Kinda forgot about this issue but it got fixed now in the new 1.18.1 version. Not sure if I will have the time to backport the fix to 1.16.5 though.

one of the Valhelsia devs recommended I open an issue about it
That was the Forbidden and Arcanus developer himself asking you. :)

Anyway, it should be a fairly easy fix, it's an unchecked cast to ServerWorld here:

The fix is to literally just swap that line with the line below it (and indent appropriately), so that the placeEntity call is inside the isRemote check.