Something similar kept happening to me last year, constantly disconnecting no matter what I tried. I thought it was a gluetun issue so I stopped using docker and tried the official ProtonVPN app, openvpn, wireguard and community version of protonvpn, I tried switching from arch to ubuntu on my NAS and the same thing kept happening.
I was convinced it was a hardware issue so I tried different hardware, same issues.
The only thing that fixed it was reducing the number of torrents I had seeding. At the time I had ~500 and once I lowered it, I stopped disconnecting.
Now I run 3 gluetun containers with 1 qbittorrent container connected to each and they each have ~400 torrents seeding and I haven't had any issues since.