When did Ctrl+Z stop working in exactly the one app I need it in?

Ctrl+Z has stopped working as undo in one specific app I use regularly, even though it still works fine everywhere else on my computer, and I can't recall exactly when this started. Could this be a setting inside that app, a keyboard shortcut conflict with another program running in the background, or something that changed after an update, and how can I get undo working again in that app?