I installed OpenVPN in Raspberry and in a HP Proliant and I have the same problem.
- Connecting to OpenVPN through my telephone 4G net is possible to connect to OMV
- Connecting a tablet or computer with my telephone tethering is possible to reach OMV, in wifi or bluethoot mode
- Connecting a computer, a telephone or a tablet through Wifi (from my work, hotel or free) I can navigate, google.... search which is my ip and checking that is mine, but I can't connect to OMV. I can work with the folders connected via "connect net folder" (Windows)
If I use Zerotier I don't have any problem.