Can't type letters in PIN when logging into Windows

Good morning everyone,

my apologies if this question already exists somewhere, I just couldn't find this specific problem.

When I recently tried to log into my computer, I noticed the PIN field wouldn't accept letters anymore. This is weird as typing numbers still works. I eventually managed to log in by using the Windows password option where typing letters and numbers works perfectly fine. The keyboard can't be the issue cause I'm using it now to type this message and as I said, switching to password option works. The problem literally happened overnight. Unfortunately, I can't remember if Windows was updated before switching the computer off the previous night.

I then went on to try and change the PIN to all numbers but even that doesn't work as I experience the same problem when being asked for the old PIN. Any suggestions what may cause this issue?

Thanks,

Christian