Silicone Case and Mute Switch
After several months I began to frequently miss calls on my iPhone 11 Pro. The mechanical mute switch seemed to activate on its own. I puzzled at this problem for a year and now I know the cause. The Apple silicone case is just flexible enough to push the switch off whenever it is squeezed a little in my hand or pocket. This may be a defect in my case or in other silicone cases. My case is now unusable.
iPhone 11 Pro, iOS 14