iCloud backup doesn't work after restore

Two months ago, my kid's iPad needed a restore with PC https://support.apple.com/en-us/HT203122

I successfully restored it with the latest (that time) iCloud backup copy.

Since that time, I can't to do iCloud backup. It doesn't start automatically. If I run it manually - it never ends (I wait for an hour and have no result and have no "progress bar" changes for an hour).

Also, after this restore ProtonVPN app doesn't work (but I have VPN on my router now and no problem with other devices).

My iPhone successfully complete iCloud backup today for 3 minutes in the same WiFi network.

P.S. Another kid has a same iPad model, with the same iPadOS 14.2 and have no problem. This iPad never needs a restore.