Clean HDMI not working on 5D Mark III

I'm trying to get some clean HDMI coming out of my 5D Mark III, and it just does not seem to work. What am I doing wrong? It wouldn't work on an older firmware, so I upgraded to 1.5.3, and it still does not work. Now I don't even have the option to switch between mirroring or not as I did with the earlier firmware. It works with my 5D Mark IV no problem. Why not the Mark III?

Unfortunately I can't help you with your problem but I just wanted to say how incredible your photography is! You must be traveling constantly.

Pinto wrote in post #18643284
Unfortunately I can't help you with your problem but I just wanted to say how incredible your photography is! You must be traveling constantly.

Thanks so much! Yes, I do travel almost constantly. I'm on the road for my photography about 300 days per year.

As for my original question, I think I've found the problem...I can get clean HDMI when connected to an external monitor, but not to the Elgato Cam Link device that I was hoping to use. So apparently the Cam Link is not fully compatible with the Canon 5D Mark III, unfortunately.

Wow, that is a lot of travel. You must enjoy it.
I'm glad your mystery is solved and you found your problem.