Backlight comes on if watch is tapped or flicked.

I have had my fenix 5x plus for about 3 months and it has been fantastic but I've noticed my backlight doing some strange things.  Sometimes I notice it is on and to switch it off I have to press the backlight button and them the back button. I have set all backlight options to 5% and all gestures to off. Sometimes it seems to be working fine then while scrolling through the menu it becomes very bright again and I cannot turn it off. It can sometimes turn on if the watch is tapped with a finger or my wrist is flicked??

Any ideas?