@sos:
I've reset my pfSense setup back to factory default, and just re-set up my openVPN server using the wizard, before setting any other services or firewall rules up.
Glad to report that all is working, using my android phone and linux clients, via a 3G connection.
As I carefully rebuild the rest of my configs, I'll keep checking functionality and may retrospectively be able to figure out what caused the issue in my case. Perhaps there was some stale firewall rule or state. Will report back if I find anything, but in the meantime, thanks for all the suggestions.
Yesterday, I did the same: reset to factory defaults -> start new configuration with openvpn-server first and now it works ???
After setting up the ovpn-server, I reconfigured all (nat-)rules, snort, webproxy, vpn-clients, outgoing vpn-failover and wan-failover and did a connection test after every single step, without any errors. Now the configuration is exactly the same as before and openvpn-server is reachable. So I
have no idea what the problem might have been.