I noticed a weird thing. I an using permanent Wireguard VPN connection (to my own server). This means, I have always-on VPN connection and enabled blocking connections without VPN under VPN settings.
I am also using SeedVault backup.
I noted, that when SeedVault finishes backup, my VPN connection stops working and I loose internet connection. Then I need to go to the Wireguard application and first disable VPN and then enable id - and everything starts working back again.
I found this behaviour (and my solution) quite consistent.
Any idea what could be the problem?