The link to the repocheck.log section of the logs documentation was
added in 7d9191ee ("Small documentation reformatting and updates",
2018-04-23), but seemingly never worked. The markdown formatter turns
"." into "-" in headings.

See
https://docs.gitlab.com/ee/administration/repository_checks.html#what-to-do-if-a-check-failed
which has a broken link to
https://docs.gitlab.com/ee/administration/logs.html#repocheck.log
linking to
https://docs.gitlab.com/ee/administration/logs.html#repocheck-log
instead (just change "." to "-") fixes it.