Unable to unlock the vault in iOS app

I have trouble unlocking my vault in iOS app on iPhone 13 Pro with iOS 17.6.1
It just started few days ago and I have been searching all over for any clues. Basically, I open the app, enter my userid and password, enter OTP code and it crashes (but not entirely). I can swipe up and see it in the list of running apps, and switch to it, but it is asking for Master password to unlock the vault and keeps crashing when I do that. I can log out from the app and do it all over again, only to end with the same result. I can login into the vault everywhere else.
At one point, I switched from PBKDF to Argon2 and thought that maybe that caused the issue. I switched back to PBKDF with 600000, but iOS app keeps failing. I uninstalled and re-installed it; I even erased my iPhone and restored it from two weeks old backup (before the problem started) - all the same. Looking for any help about this - sent a whole thread to Support, but they must be very busy, because I only got two responses back, basically asking if I have done the reinstall yet. First time i login into the app it gives me just enough time to get into settings, and I tried to enable FaceID, but kept crashing even faster afterwards, so I disabled FaceID and PIN. Timeout is set to default 15 min, and I read somewhere to set it to IMMEDIATELY, but app want take that option (before crashing again). Is there a “trick” to kick whatever is stuck through? Really getting desperate.