My wife and I both have 928s. Her phone had the same problem. I had installed 8.1 on her phone and the problems started after that. I did a hard reset twice and restored her account and settings using the sync functionality. The problem persisted. I finally did a hard reset two weeks ago and installed everything from scratch. I haven't seen the problem rear its head again.
I did notice that her problems didn't start until after I installed WP 8.1 on her phone. I never experienced the problem on my 928 with 8.1, so I'm not sure if that is the reason. Since you have 8.1 installed, I'm guessing that may be a possibility.
You may be thinking that it is most likely not that since you have owned various 928s. Are you are installing 8.1 on your phone by restoring your settings and accounts using the sync functionality instead of from scratch? If so, try a hard reset and install everything from scratch.