[bug?] operation is removed from undo list if not successful

Confirmed, that happened for me several times (v11). With luck you can still get affected files out of the general file log, but there are cases you cannot.

If you're lion-hearted, you can try out the LogCommand add-in, it gives detailed logging for nearly everything and allows easier recovery of affected items.
It needs a bit of DO config work until ready to use though. Command: LogCommand (detailed action/items/undo csv-logging)