can't cancel in loaded or manually imported puzzles

[davitof]

In puzzles loaded from my saved puzzles list, after my first action, the undo button activates itself, but tapping the undo button doesn't do anything. Cancelling still works in generated puzzles.

Samsung S23+, Android 16

[davitof]

Still in a saved & loaded puzzle: touching a star doesn't erase it.

[davitof]

Undo worked again yesterday evening. It had stopped working for at least 24 hours. No problem in other apps. No problem since.

[davitof]

Undo has stopped working again.

The full sequence is:

1 - undo is not working for at least 24 hours
2 - undo works again for no reason I could see
3 - Android security update, thus reboot
4 - undo is still working
5 - undo stops working

[davitof]

This happens in loaded puzzles and in puzzles imported from a string, not in generated puzzles nor in puzzles created using "Manual import"