but disallowed nesting. E.g. there are a lot of anchor constructs that contain an H2. That is block level content where only inline is allowed.

(And there are also three instances where the A when missing, resulting in a NAME element).

None of the warnings occur on one of the images you're floating, but as these are also embedded in anchors, it is possible that an imbalanced anchor tag causes the BR to happen at an unexpected spot.