[Danilo Zanaga]

I have a Lumia 925 and after 8.1 (preview or Cyan), the phone freezes during night. Only a Vol - + Power restarts the phone

I've read in some forums, it is a Proximity Sensor problem

Should i send it to repair? (bought Abril/2014)

[switch side method]

Best thing is obviously a soft reset it maybe a hard reset. What I suggest is to play with the clock settings and see what point it stops the phone by going through the time

[Denis Cosarba]

my phone also freezed over night so i sent it to repair
but i read something interesting today
try

turn off calendar from lockscreen, after that i had none problems with freezing.

from here

[Kyorin]

My wife's L925 (which is running Black) with DP8.1 does something similar to this sometimes. With her phone, its just a black screen and cannot be woken up or switched on or off. The only way to get it back up and running is to hold down and power for about 15 seconds, it then reboots OK , but the time and date are screwed up, I believe it goes to the same date and time every time this happens, from memory I think it always defaults to around 3.10am and a date from about 8 months ago. After rebooting using the above method and then resetting it to the correct date/time, it will then work fine for anything from a few days to a few weeks. Next time it does it, I'll look at the lockscreen settings and disable the calendar, unless anyone has a better idea.