If you haven't fixed it yourself by now...
After a new install and openvpn up and running:
Check what related services arr running.
sudo systemctl | grep vpn
will show them.
Also check the status of the services:
sudo systemctl status ....
Also dump the firewall settings to a file
sudo iptables-save > some_file
Now reboot and repeat the above commands and check for differences.
I had a similar problem when iptables-openvpn.service was started before the network was up.
The clue to that was in comparing the output from iptables-save before / after the reboot.
Gerhard
