Cannot sync account, how to fix it?

It seems to be a common problem right now. If you search the discussions for "sync", you will find a lot of threads like this one. I don't think there is much that can be done. It seems like it might be an issue on Steam's end and it just fixes itself eventually.

I would suggest trying to manually sync a few times a day until it works.

As AllTracTurbo wrote it's common issue right now. So you should reference to the linked thread.

I will close this one to not have few threads about the same issue.