Ah, the bug was triggered by doing “game is flag” in the first level. Even after restarting the level, the undo button became completely broken
Apologies for that; this behavior was due to errors happening after trying to undo when GAME IS X is made, so I disable undoing in this instance.
Problem is, I have no idea why the undo is not restoring itself upon level restart. I will release a fixed version around mid-to-late January to fix it.
Sorry for any inconveniences. 😞