I bought the 3.0 and used it several times with no issue. Suddenly, the camera take on a life of its own now when I plug the cable into the remote jack.

I've updated the firmware on the 3.0 and somehow doubt it is a problem with the intervelometer. More likely a problem with the cable (I tried it both directions, in both ProTimer ports).

When I plug the jack in, the camera fires right away. Menus are inaccessible. When I try to run a Timelapse (M) nothing happens in the camera.

Probably a problem with the camera, but wondered if anyone has seen something similar and has an idea for a way to troubleshoot. Resetting the camera software is my next move?

Sorry if this is the wrong place for this question.

First of all, if you already suspect a faulty cable, please exchange the cable and see if that helps. That would be the most likely scenario. In the camera always make sure to have set it to "Single Shot" (not continuous).
But for me that sounds like a short circuit in the cable or Plug.

Once again, gwegner nails it. I replaced the cable and all is back to functioning as normal. Easy fix. Thanks, Gunther.