My default settings are F upgrade requests only, and then I (usually) manually request aisle-only C+ upgrades after ticketing. In this case I did my usual manual aisle-only C+ request, was somehow upgraded into a middle C+ seat, and now I'm stuck in this loop where it puts me in the middle C+ seat, I change it back to an aisle MC, and then the process repeats itself. I have since "unrequested" the C+ upgrade, but the loop continues. Oddly enough, when I manually move back to MC, the seat I had previously been auto-assigned to in C+ shows as occupied. It stays occupied until it auto-assigns me back to it.

Edit: very weird situation happening here. Unchecking the C+ upgrade box also doesn't appear to be sticking. The weird thing is, when I go in and uncheck it *again*, my seat assignment then moves to "unassigned" and I can't select a seat. Refreshing the reservation then shows me back in the middle C+ seat, and the C+ upgrade checkbox isn't showing up at all in the upgrade request screen.

Edit2: was finally able to sort of fix this using delta.com instead of the app. Once I selected the MC seat, the option to uncheck the C+ upgrade request reappeared. I assume the C+ upgrade request option had previously disappeared because the system already thought I had been upgraded to C+. Unchecking the box wouldn't take when clicking "save" on the website, but I was able to modify the request to aisle only and save that. It seems that that did the trick, since there are no aisle C+ seats to upgrade me into (at least right now) and the MC seat assignment has stuck for several hours now.

I say I was "sort of" able to fix this because my preference would be to just keep my MC aisle seat and not upgrade to C+ at all, since I find the 75D C+ cabin to be pretty bad with the lavatory right in the middle, but the website only lets me modify my C+ upgrade request to aisle-only instead of outright "unrequesting" a C+ upgrade.