Proton's problem is their Vpn client. It just seems clunky. And the problem is the Windows Wireguard application hasn't been updated in years, makes you wonder why. Still works though!
After using most VPN's in time I recently tried Proton again, so far the best VPN I've used, no issues with using on sites such as BBC where Mullvad often had issues usually with blacklisting of IP's - So far so good ...
Most of the main repos are marked as complete. It's aimed at being a minimal and barebones VPN tool. It does it's job and doesn't have any major bugs. ZX2C4 Git Repository