First i would like to apologie for any grammar mistake i could do then i may have a solution for the sync problem just today i had this issue. So i tried many thing and when i was about to gave up i decided to try the update and recovery while using the option keep all my personal data then started the recovery after that i did the ckeck for any update and rebooted Opera GX then connected my opera account again and sync all my data and there you go everything was back.
I am not sure if it's the right way because i have been jumping between 2 computers but if it is you're last resort try it it's better than creating a new account?
Hope it could help anyone,have a good day