Autofocus problem with RF 50mm f/1.2 vs EF 50mm f/1.4

It looks like his camera has Lens drive when AF impossible set to 'stop focus search', which, as the name implies, stops focus search when things are very out of focus. On a f/1.2 lens, that will be most things in the scene
I suspect the DoF difference between f/1.2 and f/1.4 was enough to get AF to work on the f/1.4 lens. You can also see that the f/1.2 lens did focus when it wasn't under exposed 2 stops (dark pelican case in the shadows in a dark room vs brightly lit kitchen), I wonder if setting ISO to 'auto' would've improved the results.

I think it's not so much the lens that's the issue, but more the default settings combined with using M mode set to 2 stops under exposure. With exposure simulation enabled, AF takes a big hit when under exposing. This is an area when Canon can improve things a lot, but they don't like to do that. Just look at how they present HTP. HTP will just lie about the ISO value it shows in the EVF. It's the photographic equivalent of setting your watch 5 minutes ahead. But the description makes it seem like it will conjure some extra DR out of thin air!