GL-MV1000, goodcloud site2site problem

Hey Guys,
I established a site2site VPN with two GL-MV1000 using the goodcloud service.
On site A it is on an fix public IP. On Site B behind an Customers LAN with NAT.
The normal functions like ICMP, HTTP(S) and even Video Surveilance are working great.
But there is one problem.
On Site A there is the central controler for a communication System (like SIP). On Site B is the Contoler for the Local Communication Interfaces. I cant establish a connection between this two devices.
Central Controler on Site A:
Lokal Controler on Site B:
Communication is via UDP Port 16384
When I check the Connections List on LuCi it seems like Masqueraded or NAT.

For example I add an Overview.

Thanks for your support.

I can only add one Picture.
Here is an Screenshot of LuCi Connections Site A

Also LuCi Connections Site B