Upload & Sell: Off
Logically I would expect shitter release cable to operate...
If your RZ is pooping on you, then need return it whence it came -posthaste- and never look back. There are plenty of RZs in the world that will certainly treat you better, it's just a question of making yourself available to meet them, and being engaging and presentable
Seriously, though, as the above FMers have said:
1. You really only need a threaded release for the lens shutter coupling itself, the body's mirror can be raised with the front shutter button. I have used the Mamiya dual release and it's very convenient but not absolutely necessary.
2. If you want to shoot with a locked mirror, be sure the shutter's "MLU" coupling "thingy" is protruding and shows the little red ring after you've screwed the release cable into it.
3. The inverse is true if you want to shoot the RZ normally, e.g. make sure the ring settles into its prior place when you've unscrewed the threaded cable release.