After switching computers (but staying on the same version of Ubuntu), I copied my openvpn configuration (/etc/openvpn) to the new system. And when I booted next time, I received a weird request during boot to type in my username and password. There was no mentioning for what purpose, so I had to guess. Additionally, there is a bug that required me to press twice the Enter key after the username and password. It appeared to be openvpn, which tried - by default - to start up all openvpn configurations that it could find in /etc/openvpn.