I'm running a variety of Ubuntu Linux distribution known as Pop_OS! and have had several issues when for some reason or another Proton VPN is not shutdown gracefully leaving me without internet but still having LAN access.
Proton VPN appears to install an IPV6 "leak" interface which seems to be the problem.
The following instructions will usually bring back an internet connection..
- Determine IPV6 "leak" interface name using ifconfig. Mine is labeled ipv6leakintrf.
- Run the following command in the terminal: sudo nmcli connection delete ipv6leakintrf0.
- (Optional) If the above command returns an error stating the interface does not exist run: sudo ip link delete ipv6leakintrf0.