So you're saying that when you're away from home not on your home LAN you can access your JRiver server? But when you use your VPN service it doesn't work?
If that's right, my near term testing advice is to try connecting by manually entering the ip address and port of your jriver server and see what happens. Try both your internal LAN address and your external public ip address, but be sure to add the port you have JRiver listening on as well (i.e. 52199 by default). Try this both when connected to your VPN to and not connected to your VPN. Try it both ways when on your home LAN and not on your home LAN. That will tell whether its a NAT reflection issue or a routing issue.
So try testing:
1) Local IP on home network without VPN
2) Public IP on home network without VPN
3) Local IP on home network with VPN
4) Public IP on home network with VPN
5) Public IP on different network without VPN
6) Public IP on different network with VPN
If 1) and 2) work but none of the others work your port forwarding at the rotuer is not configured correctly.
If 1), 2), and 5) work but none of the others your VPN service is doing something wonky with routing (like Awesome Donkey described)
If 1), 5), and 6) work but not the others, you have a NAT reflection problem where your router is not correctly routing LAN-origin traffic through the port-forwarding
If 1), 2), 3), 5), and 6) work, but not 4), your VPN may not be pushing DNS/routes which is leading to a situation where your computer is getting local DNS info from your router but can't actually access the resources because it's routing through the VPN which is outside your LAN.
Basically, those six tests will tell you where the breakdown is.