Setting change by their self

My Stylo 2 setting will change all by their self. The volume will go to 0, the ringer will turn off and vibrate will be selected. The screen brightness will drop to almost nothing. The text message alert will turn off. No one has touched the settings and it will do this sometimes while in my pocket. I will look at the phone and it says I missed 5 calls and I can hardly read the screen due to be being so dim. I reset the settings and it is fine for awhile and does it again. Any ideas ???