EOS R5 C Autofocus/face recognition doesn't work when filming in slow motion

[mmphoto]

I'm shooting with an R5c. I'm trying to film a subject walking towards the camera in anything over 24fps. and the autofocus/face recognition doesn't work. I can't tap on the screen to focus on the subject either.

Shooting @ XF-AVC YCC422 10 bit.

3840x2160 410 Mbps intra

Also using a lens converter ring.

[Stephen]

Which lens are you using, specifically? 

[mmphoto]

I tried a few lenses, but for this last shoot I was using a Canon 50mm F1.2 L USM EF Lens

[Waddizzle]

The lens does not refocus fast enough for the high frame rates. 

[AtticusLake · Accepted solution]

You might want to check out page 91 of the video manual, which describes situations where AF doesn't work.  For example, when shooting in Slow and Fast mode, or with an EF lens that doesn't have an AF switch.

Also, you say you're using a "lens converter ring" -- I take it you mean an EF-RF adapter.  Which one?  People have reported bad results when using third-party adapters, and generally recommend using the official Canon ones.