Thank's for your answer. Quiet mode was involved, I don't know why because it was still disabled.
In fact, this problem was just one point, regarding the whole big one happening for people who upgraded OTA from 4.2.2 to 4.4.2 with stock ROM.
Other symptoms encountered :
- wifi disabled at reboot
- wifi AND data icon activ together
- 3G/4G data consumption during wifi connection at home
- phone always warm, and power drain
- interface was lagging
I performed a factory reset.
Can u believe that ? : yesterday, factory reset and reinstallation. This morning at 6.50am, phone play a sound and goes out from silent mode
Looking at quiet hours : unchanged still factory reset, so it's disabled, and time/day selection is 22H00 --> 6H00 from monday to wednesday. I don't know where the setting "6.50am" is stored.
So I still haven't any clue about what brings phone out from silent mode.
list of reinstalled application:
- whatsapp ( with database restore )
- sms backup&restore
- es file explorer
contacts were stored in google account, but nothing else that I can control was restored from cloud.
Factory reset solved ( until now... ) other problems.