Why is my Nikon D3 no longer tethering/no longer visible in C1? (No Camera Connected)

Hi guys,

I've been searching the internet for answers and not having any luck! If anyone can help me, I'd be hugely appreciative!

I recently bought a second-hand Nikon D3 (yes I know it's an old camera! But it shoots beautiful images).

I had a photo shoot coming up and wanted to shoot tethered so I plugged in the D3 and did a test shoot. No problems, it all worked fine. But the next day, on the photo shoot, using the exact same camera and laptop and software and tethering cable, the camera is no longer showing up as an option for tethering. So frustrating!

The only thing I can think is that maybe there was a computer upgrade overnight that has messed something up?! Any suggestions??

Details below:

Camera: Nikon D3 

Software: Capture One 12

Laptop: MacBook Air (early 2014)

OS: macOS Mojave (version 10.14.6)

Tethering cable: Tether Tools

Note: I've already tried a few things, including changing the USB settings (Menu > Set up menu > USB > change to M/P). I've also tried basic things like turning the camera on and off. Turning the laptop on and off. Trying different USB ports on my laptop. Trying all of the above in different combinations. 

Note: the camera's firmware is up to date (2.03) according to the Nikon website. 

Note: The D3 is showing up in the laptop's Image Capture app but not in Finder. Not sure what that means??

Note: One thing I've only just noticed right now: in Capture One Pro preferences, in the Update tab, the Nikon D3 and also my other Nikon d800 have been moved from the heading "registered with update notifications" to the heading "unregistered." Don't know if that has anything to do with this? [UPDATE: I checked again and both cameras have moved back up to the "registered" heading. Who knows why.)

Thanks in advance for your help!

Bex