It's true that in the future I would do some more thorough testing, but never-ever for this legacy application can I build a bullet-proof automated testing solution - there will not be a budget for that for sure. However, even with a fancy solution mistakes will happen and you still can't stop release propagating. It's just a matter of time when it happens.

"A bullet-proof automated testing solution" isn't needed for the type of problem you describe. Anything that logs in (including a human on a real device) would catch it even if it does nothing else.

Exactly. It’s a poor excuse that the author didn’t even try to log in to the app with the newest version.