I'm not sure about containers, but in Qbittorrent, Settings, Advanced, there is a "Network Interface" setting you can use to force qbit to only use a particular network interface. My VPN has it's own network interface, so if it drops out, qbittorrent just stops downloading until the VPN comes back up. So, no IP leaks. Hopefully this helps you out a bit!

Do you use docker compose?

https://www.youtube.com/watch?v=xbSfaKwyfXE&t=33s

version: '3.7'
services:
  gluetun:
    image: qmcgaw/gluetun:latest
    container_name: vpn
    cap_add:
      - NET_ADMIN
    ports:
      - '8080:8080'
    environment:
      - VPNSP=protonvpn
      - VPN_TYPE=openvpn
      - OPENVPN_USER=xxxxxx
      - OPENVPN_PASSWORD=xxxxxx
      - REGION=United States
    restart: unless-stopped
  qbittorrent:
    container_name: qbittorrent
    image: cr.hotio.dev/hotio/qbittorrent:latest
    network_mode: 'container:vpn'
    environment:
      - PUID=1000
      - PGID=1000
      - UMASK=002
      - TZ=America/New_York
    volumes:
      - '/home/xxxx/qbt:/config'
      - '/home/xxxx/INCOMING:/downloads'
    restart: unless-stopped

That should get your started