Swarm Agent "Channel not transferred" error

I’m trying to set up Swarm using 3 machines, with one as the coordinator.
It will work to the extent of finding other machines and sending them jobs, but one of them (not the one the unreal project is on and not the coordinator) is getting stuck in a loop, showing this error message:

This is the setup I am using in all swarm agent settings:

I’ve made sure that nothing else on the PC throwing that error is using port 8008 or 8009, cause that’s the closest issue I could find as far as troubleshooting.

Does anyone know what this is about?