Can't shoot tethered while CF card in camera

Hi

I've just upgraded to a new MacBookPro with Ben Sur and installed the latest Capture One 21.

I plugged my Canon 5D MKIII into the laptop via a tether tools cable. The images won't go through to Capture One while there is a CF card in the camera. It only shoots tethered when there is no card in the camera. I find this very problematic. I like to have a card in the camera to catch any images that may not make it through to the laptop due to cable mulfunction or cables accidentally falling out of sockets. It has always worked great in the past being able to shoot tethered while having a card in the camera. It don't need it to shoot to both simultaneously, I just need to know that if there is a cable issue then the image will be caught on the card. We you moved around alot while shooting then this does occassionally happen. Not the snuggest fitting port on the Canon, even when the cable is gaffer taped to the camera.