After installing a new SIM-card, my Fairphone 4 didn’t accept my screen lock-PIN. On the screen lock it showed the message “Nach dem Neustart des Geräts ist die Eingabe der PIN erforderlich.”
I had the PIN saved in a password manager, so I was 100 % sure, that this was the right PIN. The SIM-PIN for the new card got accepted. The problem was the screen lock.
After several unsuccessful tries I remembered, that I did change the screen-lock-PIN a long while ago to the SIM-card-PIN, so I had to remember only one code. So I tried the first PIN I used before this change on the phone - and it worked!
My guess is, that maybe because I took out the battery to change the SIM-card, the Phone somehow resetted the PIN to its first value?
I hope, this will help others with similar problems - and I am curious, if someone else got the same problem.
Best regards
Claus