You're combining vendors. We cannot comment on how the receiver and sim interact. If the transmitter/receiver combination works when servos are plugged into the receiver, then the problem is in the device that's external to the receiver.

It may be that the receiver isn't quite compatible with the transmitter. We don't know.

We can only advise about Futaba equipment. If the 14SG transmitter works nicely with the supplied Futaba receiver, then the problem's not Futaba's problem.