The problem:
It’s impossible to change the Screen Color in NXTVISION as Visual Enhancement is grey instead of black.
Just by repeatedly trying in the end to get into Screen Color I was offered 3 choices in Screen Color. Advanced wasn’t listed. Of course I choose Natural and the reboots are gone for now.
The same approach worked with 2 other users I had contact with. Just keep trying.
Without changing anything, it seems like reboots have stopped. I haven’t had any in 2 or 3 days now.
Edit: I sent this comment and 20mins later it reboots twice. Freaking jinxed it…
I am very sorry for you
Still have reboots, still can’t acess the visual enhancement section because NXTVision keept crashing.
Contemplating a clean install, but rather have a solution without starting over…
I understand totally! Let’s hope they come up with a new release of update 
New patch just dropped, and the patch notes say it fixes random reboots! Let’s see how it goes
New update you mean?
FP4.QREL.15.15.2 just arrived here. No Problems so far. Deutsche Telekom, Germany.
If you installed it, please comment us how it behaves, and if the problem with background apps still occurs. Thanks in advance.
I don’t see any upgrades right now…
Thats not the topic here and no this was def not fixed
As far as we know now the upadte was recalled, as it was not intended to roll out yesterday to the public.
That might explain why I couldn’t find any mention of it in the release notes… too bad, I already installed it this morning.
I already found the NXTVision reset to effectively fix the random reboots earlier, so I’m only hoping this doesn’t break anything new.
Not sure about background apps, but since I installed this about 4 days ago. I haven’t had any random reboots! So it seems to be working.
FP4.QREL.15.15.2 saved the day!
Thank you Fairphone, no more self reboot since the update! 
Update FP4.QREL.15.15.2 solved the self reboot problem on my FP.
With 15.15.2 I have no USB Data connection to my PC. Only charging works. Does it work for you?
Hello @KleinerAdmin , I just connected to my PC, no problem to activate the USB preferences “file transfer” (by default it is charge mode).
Sometimes USB cables can be deficient for transfer mode but OK for charging, did you try a trusty cable?
Thank you for your reply! My cables always worked before and work with other Smartphones. I should try a restart, but fear a brick. I’ll wait some time.
oof just had another random reboot after almost 2 weeks without… well at least they got less I guess?
Interestingly, this happened shortly after landing in another country. I wonder if that’s somehow related