I solved this issue by disabling [email protected] (deprecated), removing all configuration files from the OpenVPN root sir and moving them to the server dir, as well as activating the respective [email protected].

I initially worked around the issue by putting the following line in my rc.local:

systemctl stop [email protected]

I finally solved it by disabling the deprecated [email protected], removing all configuration files from the OpenVPN root directory and moving them to the server directory, as well as activating the respective [email protected].