Problem with (old) Unity Master Server and NAT Facilitator

Hello,

I'm unable to connect two devices together using the old Unity Master Server and NAT Facilitator, installed on our own server. What I'm doing is start a server on both devices, register both to the Master Server, and then have device A connect to device B. (The reason for this two-way setup is that I can then try the other way around if the connection fails for some reason.) However, device A always gets the error message:

NAT target 152667890 not connected to NAT facilitator [our...

Problem with (old) Unity Master Server and NAT Facilitator