My local sync works perfectly under all but one condition - when I am running the VPN on the phone.
To be clear, as soon as I disconnect from VPN on phone it will sync perfectly with laptop which is running as server and is itself connected to VPN (same SW and account). So we know the network configuration is correct and that neither firewall nor VPN on the server side cause issues.
It is literally only when the phone client is connected to VPN.
Yep, with a VPN you are in your virtual private network and your notebook is in a different network, so it’s not reachable for your phone.
You can think of it like this. Your notebook is connected in your local network while your phone is located wherever your VPN provider is located.
Likewise you won’t be able to print on local printers when connected to the VPN.
That being said, some VPN solutions allow local access but that depends on your VPN client. Sometimes there is a setting you can disable. The behavior you describe sounds like the setting “redirect local gateway”.
Maybe the VPN client allows adding excludes for hosts or apps so you could add an exclude for the IP of your notebook.
Or just use ESS.