Actually I forgot to mention this: did you try to reset the network settings? There is an option:
Settings/Backup & Restore/Reset network Settings (down to the bottom)
and maybe do a phone restart immediately after.
I am translating it from Italian, so it might be slightly different. I did it a couple of times already, with the first being soon after I synched the XC with my M2. Doing so it doesn't just removes the APs and BT devices, it also rebuilds some configuration files.
I must also say that after my post above I didn't get the issue again. Like with the brightness, that now seems to work (it doesn't go to 0 anymore on dark environments).
