My joy was short-lived. Less than a month has passed since that post and random reboots came back, with the new battery. Yesterday I took the phone out of the pocket to see it rebooted and stuck on the "enter SIM card PIN" screen three times. And the day before that too. It does not usually happen in the shirt pocket, but is guaranteed to happen in the trousers pocket. So I assume vibrations caused by walking (or maybe flexing) have something to do with it. I cleaned the contacts again and as a last resort, will try the paper to prop up the battery. If that does not help, then goodbye Jolla, I cannot afford to have a phone I cannot rely on.