Thanks I have installed all 4 firmware in that order again. Just in case, I have only 2 of the 3 external drives connected now. We will see if it happens again.
Update! Almost 3 months later and the factory reset didn't occur anymore after reinstalling the firmware from 2.0.1 up. I have to admit I havent been using the Q10 as much anymore (1-2 times a week) though, but I'm satisfied so far. I haven't installed 2.0.8 yet.
This has happened to me a couple of times recently. I got a new 4a PSU (Leicke) and it happened again today using that. It appears to happen as the main Android screen appears which is leading me to think that it might be Pcristi's utility "Mount Storage by UUID". This possibility popped up earlier in this thread. Does anyone else using this get the same problem? I'm reluctant to switch back to not using the UUID mount as it means reloading my library again from scratch.
For me it happened during the Boot sequence when it shows the Himedia logo on tv. Every time the reset took place, that sequence took longer than usual.
I used to use "Mount Storage by UUID" as well when I experienced those resets. After reinstalling the firmware using futeko's instructions, I did not install that utility anymore because I had a similar feeling the problem is somehow related to mounted storage. It doesn't prove anything yet, but this may be an indication.
I'm also more careful when (dis)connecting the external drives.