Your openvpn client on ubuntu doesn’t connect to your server. After “Initialization sequence complete” the process is killed.
A Log Excerpt , after the last step the process is killed
Sun Jul 8 14:13:58 2018 GID set to nogroup
Sun Jul 8 14:13:58 2018 UID set to nobody
Sun Jul 8 14:13:58 2018 Initialization Sequence Completed
Make sure that your openvpn client is latest 2.4. Ubuntu official repository gives you an outdated version. once you update, the problem should disappear.
here is how to update to the latest client