iPhone 6 plus silent switch malfunction after iOS 9.2

Hello,

After I've upgraded my iPhone 6 Plus to iOS 9.2, the silent switch began to present a malfunction.

When it is in normal position, it's alright.

When I switch to silent position, the phone starts to alternate between sound and silent mode, randomly. When it is in silent mode and you put in your pocket, you feel it vibrate randomly, and you think it's a message or other notification, but it is the phone vibrating without a motive.

Can someone give some advice? Is it a software glitch due to iOS 9.2 or is it a hardware glitch?

Thanks in advance,

Muriel