"warning: no free slot for incoming connection"

So, I have a multiplayer game that usually works. A server starts up, uses the Unity Matchmaker and Routing service, players connect, they all have a great time.

However, sometimes, just sometimes, a server starts up, and no-one can connect. At all.

So, I crank the log file up to max:

"Increasing Log level to max!"

and I start getting network messages on a per-bit basis.

SetSyncVar UAV_RemoteDrone bit [4] 0->5
SetSyncVar UAV_RemoteDrone bit [8] 0->1

And then, all of a sudden

Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection
Warning: no free slot for incoming connection

So - the server is receiving incoming connections, somewhere, running out of them (It’s set to 64 right now, and my retry is every 15 seconds, so there’s little chance it’s ACTUALLY running out)

Unsure where to progress here, and I have no info to help me debug further. This is latest 5.6, using uNet.

I also have this problem, and they won’t answer any questions about this…

I literally gave up using any Unity networking solution due to the atrocious design and lack of support.

We’re facing the exact same issue in Unity 2020.3.10f1. Does anyone have any insight on this issue?