I’m trying to take a screenshot on my FP2 slim with newest Fairphone Open OS installed. When I press both the volume-down and power buttons, nothing happens for about five seconds, then the phone reboots.
This can be reproduced every time, and happens also immediately after startup.
Some people had problems with random reboots when using the new slim cover (see here). To swap the power and the camera button seems to help. You may try this or contact support.
I do get random reboots, but most of the time when I have scrolled through a list for some time, stopped to read something and then resume scrolling. I’ve had the same on my HTC Desire before, so I didn’t get suspicious about these, just rolled my eyes a bit.
I see that the reboots happen when pressing the power button for a long time — that explains at least that part — but I wonder why the screenshot function isn’t triggered here if both the power button and volume-down button presses are registered correctly.