losing sound except incoming calls

My iPhone 6 occasionally loses sound alerts for incoming texts, calendar reminders, the sound when using the keyboard, basically everything except incoming calls. It can be fixed by powering down and back on. It may go a couple of weeks without the problem, then happen up to a couple of times the same day. My first iPhone (purchased about 2 years ago) had this problem, and I visited the Genius Bar a few times, trying multiple things including resets, before they finally just replaced the phone. The second phone has been doing exactly the same thing, while my wife has never had a problem with the same phone. Has anyone else encountered this and figured out a fix. The phone is running the latest update.