What is the issue with the HTML Standard?

If two history traversal to the same entry are interleaved, and the second one is bound to fail, the former will remove the upcoming method tracker from navigation, and the second one will re-enter #navigation-api-method-tracker-clean-up in #performing-a-navigation-api-traversal from step 12.2, 12.5, or 12.6 depending on rejection reason.

Re-entering #navigation-api-method-tracker-clean-up doesn't have any adverse side effects per se, but it does assert that an api method tracker being cleaned up should either be ongoing or upcoming.