Where did you read reports of this? Or is this your personal observation? Not sure if it's the same problem that you're describing, but I've been struggling with an issue with my R5 and RF200-500 (and also my RF70-200, I believe), where I was unable to fire the shutter sometimes in AI Servo, continuous drive. After this happened enough times, I realized it wasn't even letting me focus during these times, even though I had a large object with plenty of good horizontal and vertical contrast. I started with 1-point AF, then went up to Expand AF area, then Expand AF area: Around, Zone AF, and finally Large Zone AF: Horizontal, as I couldn't figure out why it was randomly unable to obtain any focus points. Focusing would fail with all of those modes...some days I would have zero issues, some days it happened multiple times. But the day it happened frequently (during 5 out of 20 subjects), I did notice it was locking out the focus at the same time in each pass of the subject...so all at the same distance. I would be able to lock on while the subjects were far away, then my AF and shutter locked out as it got closer, then I was able to shoot again as the subject passed me and got further away again. And to anyone wondering, no, my buffer wasn't filling up...I only took about 3 photos each time, before it locked up on me.* AF improvement.
To address the case where focus freezes at a given distance & won’t refocus on a new target (often closer & larger & under the spot focus square).