I have a Nexus-5x and I rarely restart it. I'm using fingerprint and password for authentication, usually just fingerprint but once in a while I have to enter the password for safety. This just happened and my password was not accepted. When intentionally entering a wrong password it would just say 'wrong password'. But when entering the correct password, the screen would go black but the lock screen would then just reappear.
Rebooting worked but I'm still worried, why does this happen?