i have had a nightmare booking my ADR's this year! I can laugh about it now that they are done but I was screaming at the laptop on sunday when i tried to change one!
I can log into the website from my lappy and no reservations show at all. They show if I use the ap on my ipad though I managed to get it sorted on the ipad app - i gave up on the website!
I had this exact problem. I kept logging in and out and trying to book different restaurants and start from different pages, and eventually it worked. Booked a fee online and after one went through it got easier. But it was still much easier to do it on the phone though. Had them all done in minutes, and they all appeared on the my disney experience app immediately.