I also see the same problem as @pleveille.
I have two separate iPod Touch 6th gen, running
iOS 11.1.2
and
iOS 11.2.2
Both with OpenVPN Client Version 1.2.5, and both show the same black-screen.
Both used to work OK with OpenVPN Client 1.1.x
CONSOLE LOGFILE AVAILABLE HERE:
https://s3.amazonaws.com/anon-o-mus/openvpn-console-log2.txt