Default [Q] LG switches alone to silent profile

LG G2 D802 4.4.2 software D80220b-HKG-XX

My phone switches to silent profile more than 10 times a day without any action. Usualy after a certain time of stand by...
Quiet mode/quiet time not activated. All gesture function disabled except Knockon.
Have you heard about that ? Any solution?
Thanks for help