iPhone 13 Pro keeps silencing calls & notifications

For sev mos my iphone 13 pro max goes silent even though mute switch isn’t on & haptics/sound setting is set to control with buttons & set to highest volume. I miss calls & notifications constantly. To fix it I have to turn off control with buttons & turn it back on again but it keeps reverting to silent mode after a few days. I have sev friends w/iPhone 13’s who have same issue. Any ideas as to cause or how to fix?