Not entering a password when opening the app is not the same as not having a password. It's quite normal for your phone to remember the password for an app so you don't have to enter it every time, and when that app is then updated to a new version the phone is no longer able to find the associated password. As an example, every time the Nord VPN app is updated I have to reenter the password on my phone, but then the phone will remember it until the next update.
Obviously, with more sensitive apps like mobile banking apps, you will have to enter your password every time for security reasons.