I bought an R5 six months ago and recently it started misfiring while using strobes. It's happened with Profoto, Godox and Elinchrom so I know it's not the lights. Every 10-15 photos I take, the focusing box on the back screen stays white instead of green and the shutter audibly slows and sounds kind of crunchy, like it's skipping a beat. The photos turn out dark even though the strobes go off, so it's like the camera isn't taking in light fast enough. This will last about 5 photos or so, then go back to working properly. I also use a Commlite mount adaptor for my lenses so not sure if it's that or the camera.
Anyone else struggle with this or have a solution?
It could be the adapter. If you switch the lens to MF and the issue persists, then there could be an issue associated with the camera. Ditto for an all manual lens. If the issue goes away when manual focusing, then there could be an issue associated with the third party mount adapter.
I would agree with Waddizzle on the information they've provided for you to test on your end. We would suggest to test a Canon RF lens with the camera. If possible, please also test a Canon Speedlite flash since it appears that you are using third party flashes and strobes. This will help in determining if there may be an issue with the camera itself.