Seems vaguely similar to my “no way to turn it on again” issue, but also kinda different. According to what I read on Fairphone’s documentation, you need to get to the point where the Fairphone logo is displayed in order to switch to safe mode? So it means that at least your phone accepts to be turned on?
These booting issues worry me the most: What will happen if I have to do the whole “remove the battery” operation for the first boot after the next upgrade? Dunno if this’ll have a nasty impact.
And since there has also been reports of “aeroplane mode messing up with Internet until reboot”, now, at night, I just mute the phone and use the battery saving mode instead on turning it completely off.