Few days ago, I was trying to reclaim my Mclaren F1 GT 1997 from auction. While loading to reclaim the car, the game just crashed and turned off itself. So I turned on the game right after that happen. I checked my auction, there was no my car and garage.
I have not experienced the lost progression (or game stopped saving) since November and what you have describe looks like it. The servers registered the claim but the game didn’t save it. I guess is gone for good, unfortunately.
About the only thing you could do to try and get it back is submit a ticket to Support.
This happened to me about a month ago. Car just vanished and I never got it back.
To me it happened when i was buying from forzathon shop a bugatti eb110, i tihnk.
It said it failed and it will try to added it later or something. As exepcted nothing happened. Lost the handreds of FP.