I am no expert like some of the people on here. So take anything I suggest with a grain of salt. I have all Mac or apple environment. A while back I had something similar to yours. Like I said I turned off the VPN and it helped. It did not stop it all the time. What I figured out is that Apple has been doing updates at a rate I have never seen before, in the last year I think I have had 3 or 4. I am sure that no one else is keeping up with the rapid change's Apple is making in software. Hence I think some of it is Apple and some of it is in the cox email software. I would never do a total wipe of my computer and start from scratch. You need to find someone in Cox upper level who understands what you are going thru and design a path to fix it or at least help you on who to go too. What's funny is I hardly ever have any trouble with imac's or Mac books it is mainly with iPad's now at least twice a week I have to do the 2 factor thingy on all ipads to keep them where I can check my mail. I have went thru and corrected everything I know to cause clashes and I know think it's a two party problem.
Somebody here, at Cox upper level, or computer software will find a solution. The problem is how long is it going to take.