Any 5D mk4 owners here.

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Using my 54d with fast lenses I notice considerable variation in focus accuracy (OVF)

My 100-400 seems to nail focus every time but, even when tripod mounted, mirror up and 10sec timer, my 300 2.8 will hit about 5 of seven shots.
It's a similar story with the 85 1.2.

When hand held using continuous high speed shooting I also get a lot of focus misses. Looking at the images in canon DPP the focus point during a 10 shot sequence stays on the subject but the actual plane of focus moves.

This is probably just my imagination but the AF system does not seem to like the colour red.

Has anyone else encountered similar behaviour?

If I can muster the enthusiasm I'll post some samples.