Have a Canon R5 and a couple of manual lenses that I couldn't get to work with it at all. Turns out it is the setting "Release Shutter w/o Lens" -- works great now. Putting this out there for anyone else with the problem.
https://cam.start.canon/en/C003/manual/html/UG-08_Custom_0030.html#Custom_0030_4
@piratenpanda I've overall been really happy with it. This was the last thing which was really frustrating me.