I also haven’t had much success with the incognito mode that is frequently suggested on the Dis. I do better just giving up and trying later. Not really an option though when you are in parks.
Yesterday my husband’s space mountain FP vanished into thin air. The other FP’s for both of us on that day were still intact. Tried everything website, ME, incognito, refresh after refresh, you name it. I had a printout of the FP’s so I knew I had booked it at 60 days. I realize that it was still there but it is so random what happens. I had better things to do so returned a few hours later and it mysteriously appeared. I’ll be bringing my printout but IMO MDE isn’t reliable which is sad when Disney touts it so much. I had many issues linking my Dolphin reservation. It was fixed on the Dolphin side, never on the MDE side. I called Disney and spent a bunch of time getting them to make manual Fp’s that can’t be modified. Lovely.