There’s at least one major bug filed about UNDO–
vassalengine.org/tracker/sho … i?id=12554
And a very current thread with discussion of several other reproducible UNDO problems:
https://forum.vassalengine.org/t/about-bug-12554/10656/1
If you end up able to make a “minimum demonstration module” – a stripped down module that reliably reproduces the problem – then that would probably end up being useful.
Brian