That's recommended by glutun.
https://github.com/qdm12/gluetun-wiki/blob/main/setup/providers/protonvpn.md#protonvpn
You'll need to whitelist localhost authentication in qbittorrent settings as well.
Ive been successfully using that exact stack for a few months. I'd recommend using wireguard instead of openvpn.
Also, add a the gluetun health check and add condition: service_healthy to your qbittorrent dependency.
You can also simplify your port forwarding quite a bit. Here's a link to how I have it setup. Qbittorrent won't start until gluetun has a healthy connection. Then it repeatedly runs your port forwarding command until it gets an OK exit.
Port forwarding for torrenting shouldn't affect your webui accessibility so it's also possible your qbittorrent is failing before gluetun comes in.
How is Detroit? I'm a barely gamer SO trying to find a co-op game that I enjoy