Maybe I misunderstand the firmware portion of your comment. Is the setting to update the firmware automatically not working? Do I need to do anything else to make the update work?
From my perspective, I agree to the fact that something must have changed outside the printer. It was working and without a change, it stopped. The only thing that would come to mind is that the printer's certificate might have expired, but I checked this and it is valid another 27 years. ;-) However, the printer's certificate is not issued by a CA, but self-signed by the printer and the message: ssl server certificate untrusted points to this. How would I get a CA signed certificate and install it in the printer to be used by the printer? Or can you rule out the certificate thing as a reason for this behaviour?