My Jolla also was in a boot loop. Option 5, repair btrfs worked.

I don't know exactly why the device was in a bootloop. I tried to stop my bluetooth leaving my car. At the same time wifi tried to connect at a known network from a friend. When I was inside the house I tried again to stop bluetooth. The bluetooth 'light' in settings kept blinking. Then my Jolla didn't react anymore. Power down and power up resulted in a boot loop.