Intermittent OpenVPN problem - traffic does not go through VPN

[madbrain]

I setup OpenVPN from one of the video tutorials found on Youtube. I also setup FreeDNS dynamic DNS.
I use an Android client (Galaxy S22 Ultra).

When I put it in cellular mode (turn off Wifi), the connection usually works, as long as I'm at home.

Things turn out differently when I'm on the go, ie. when I really actually need the VPN. The VPN client connects to my host properly. But then, 95% of the time, that's the end of it. No traffic goes through to any of my hosts.
Sometimes, if I reboot my phone, the problem is fixed, but most of the time, it is not.

Does anyone know what could be causing this intermittent failure, or what it might be ?

I'm considering setting up another type of VPN since this seems to be unreliable. What would be recommended ? IPSect ? WireGuard ? And where should I start for setting up some simple remote access.