Thanks for the fast reply! I will look into it.
EDIT:
For future readers: the link above was exactly my problem. I fixed by delaying the health check to 2 minutes. Apparently this is used for OpenVPN only anyway. Since I use Wireguard it doesn't matter.
I added the following line to the environment in the gluetun docker-compose. 12 hours it's still running perfectly.
HEALTH_VPN_DURATION_INITIAL=120s