If you have associated domains enabled, the autofill feature is used, and then you get a UIAlertController that asks you to save or update the password.
The problem is that if the user puts applications in the background before tapping either the 'Update Password' or the 'Not Now' button, the keyboard for text fields is no longer shown after switching back to the foreground.
I reproduced this in several apps, which seems like an iOS Bug. This appears to be an old issue as well (see https://stackoverflow.com/a/61165107/9435282)