Pinephone doesn't accept PIN number

I havent’t changed the PIN number of my Pinephone. So it’s still the default number. But suddenly the system doen’t accept it anymore. It happened already once some hours ago. But after a while (or after rebooting) it worked again. But now nothing helps. I simply cannot unlock my phone anymore.

I rebooted several times, but to no avail. Is there a way to re-set the phone to delivery status?