NOTE - please read update below and all comments.
I have a Mavic Cosmic carbon wheel which is perfectly true, but it has some vertical hop (3-4 mm). I thought at first that it was out of round, but deep carbon rims are very strong and rigid, and I don't see how it's possible for it to bend.
I did a test to check the roundness of the wheel - I measured the radius at different points around the wheel (from the hub to the outside of the rim). It was 306 mm all around. So the wheel is round, right?
I took the quick-release axle out and rolled it along a flat surface - I noticed that it is slightly bent, maybe 1 mm max deviation. I guess this is at least partially contributing to the hop, but I don't think it fully explains it. I will replace the axle - hopefully that corrects the issue, but if not, what else could be contributing to it?
I've replaced the quick-release skewer. The wheel still hops, so at least it's eliminated that possibility.
Here's a video showing the hop. https://imgur.com/a/icMfN7q
I've also noticed there is a slight raised area at the edge of the wheel at one point. This is on both sides, like the wheel edge is slightly "flared" at that point. This is very slight but enough to alter the braking force at that point - I can feel pulsing through the brakes as the friction increases at this point. Looking at the wheel rotating again, it seems to pull in sharply at this point. So it's like the opposite of hop - what's that, dip? This causes the excessive rubbing and you can see the brake marks below: