Sorry, I meant to say it happened when a call was coming in and I was on Internet the msg. would pop-up an I couldn't answer the call. Would hold power and lower volume down until restart and called the person back. It was maddening. Thanks
Thank you! That seems to have solved the problem for me (Note 4, upgraded to Android 6.0.1, on T-Mobile).
I had tried clearing the Phone app cache & data and also the cache partition with no luck.