Yesterday, my Fairphone did an apparently unprovoked Factory Reset.
It had run out of power, and when I turned it on again, a strange-ish boot screen appeared, like some custom Linux distro booting up in ASCII mode (with Chinese characters).
After reboot, everything was back to factory defaults, and the internal storage had been wiped. Messages, photos, apps and contacts stored in phone storage are all lost.
How the %#¤&%¤&%¤&%&!!! can that happen?
As for the how: The Chinese characters thing sounds like it started in factory mode (normally done by holding volume down + power, so if the volume down button was somehow jammed…). If it somehow selected ‘Clear eMMC’ it will wipe the internal memory, but then it shouldn’t be able to reboot into a working system - so I’m not really sure what happened to be honest. EDIT: this does actually reset the phone to factory settings, see this video.
As for lost data: If you were using google apps and were synchronising to your account, your contacts should be stored in the cloud, as well as a list of apps you had installed. The rest of the data is more problematic - other forum users have started topics about recovering deleted data, but I don’t remember any success stories. If you do want to dig around for solutions, then keep in mind that you have the highest chances of success if you keep your phone switched off in the meantime, as any use increases the odds of any recoverable data being overwritten.
Volume down + Power creates a screenshot.
Yes, when booted it does… but if you’re booting the phone up from cold it goes to factory mode (slightly different to the recovery mode)
Ah, my misreading! 
Easily done, not to worry. It is confusing all these button press options 
If you are to connect the phone as usb storage and have a linux or OS X pc at hand, you could try the tools testdisk and photorec to at least recover the deleted pictures from the phone.
Turns out clear eMMC does do a factory reset: For an illustration of Factory mode + reset, see this youtube video: How to Factory Reset every China phone with chinese Recovery. (I’ve updated my previous post). As said, maybe the volume key got stuck on the phone on cold boot, and unluckily this option got activated as a result. If anyone else ends up in factory mode due to the phone having a mind of its own, the safest way out is probably by removing the battery.
Carsten_Agger, I hope you can recover data, let us know how it works out if you give it a try!
I have slightly different problem: My fairphone has reset itself to factory settings four times in the last five months while powerd (and not in use). I have no clue what’s happening.
I had a similar experience yesterday. I wanted to boot into recovery to clear the cache, because of some software problem I was having. Of course I held the wrong volume button, so I ended up in factory mode. Because the volume down button was still pressed when I entered the menu, the selector moved down a few positions. Next I wanted to press a button to get the hell out of there, but the button I pressed confirmed the selection I was on. Next screen: erasing eMMC…