I figured out what the problem was.
For security, our WebDav server has a rate limit, and it's enough for syncing but too low for restore.
Thank you for your support.
1. I tried latest version of store and website.
2. windows 10 (1809)
3. It's ok to sync on mac and android. But I haven't tried to reinstall and restore on these devices, because I'm afraid of having problems.