The antenna should not spin as you describe and I, as you do, suspect it is the problem.
I would guess the issue is the connector is not wedging the antenna post into the pot thus allowing the entire antenna to spin. I would remove the antenna and see if the inner metal post spins freely. If it does not, then I would work on the fitting till it fits tight.
If the internals of the antenna seem broken, you could use a short stiff wire temporarily to test this theory, just bring the receiver close to the camera since your short wire will not have the same impedance as the designed antenna. I don't guarantee this will work and confirm the antenna is the issue, but if you like I will test it and report back. You could also carefully remove the protective outer film and reconnect the conductive inner as a test also.
I broke my antenna and then repaired it carefully this way. I soldered the break and used heat shrink tubing of multiple sizes to reconstruct the outer skin.