I am not sure this is the same issue, but I played quite a lot with transmissions and ADF using the MI8. I am back to the game after a couple of years, so my experience might not apply to the current release of the game. Anyway:
the issue to me was like this:
when the transmission start it is properly transmitted to all the clients in the server. However, if a client connects after the transmission starts than he cannot receive the transmission. I found 2 solutions:
1) just start the transmission when all the client are in the server
2) do not use loop on the transmission. Make it start and end, then wait for a second and make it start again. This solution always worked for me. I think you can also do this using the ME without lua, although using scripting and MIST it comes easy.