I've run 2080Ti SLI and single card with surround now for a while (since about mid October) with no issues. However I have not played BF5 so I have no info for you there.
No, I'd never sell an item that was not working properly--I'd just RMA it. The only reason I am selling this is, as stated above, is that NVlink + SLI is really underwhelming. I have TWO of these cards right now and I don't need both as the performance isn't worth the investment for the games...
Also running 3 x Dell 144Hz monitors in surround with 2080Ti cards.
OP, which particular monitor are you using? There are many reports of problems with BenQ monitors and 144Hz because of "timing problems" according to Manuel over on the Nvidia forums.
I think that's a great lesson though for all of us when running in to problems...reset everything to stock and move from there. Glad you seem to have things figured out though!
I specifically have not been installing the USB C drivers since I got my cards and haven't had an issue yet. Obviously this is just anecdotal but when I saw those drivers with the install package and I knew I wouldn't use them, I simply omitted them.