Two agent calls at once, and the second had nowhere to send the map

We fired two agent calls together and the second session had nowhere to send the map. Is the remote player single-session?

Yes. The remote player allows one active session per process, and the host transaction has to be started on the host. If the player has nowhere to send maps, check global settings and that the transaction is up. Plan agent traffic around that one session. This is not a pool of 3270 emulators.