I lost all my RTTS progress due to this same stupid error.
I haven't restarted because I have the slightest (probably complete waste) hope that it can somehow be restored...
I tried deleting my save files on the Xbox.... loaded the game back up, nothing. Tried unlinking the accounts on the website, still nothing. I've submitted a ticket and nothing yet, probably never will be.
It's weird because my character still is on my DD quad with 100+ power so it still has all the progress I made with my character on that mode but it's completely gone in RTTS? It was the mode I was most excited to play, and I'm not going to restart just to lose it all again.