Steps to replicate the issue (include links if applicable):

• go to the official WikibaseLexeme code documentation on doc.wikimedia.org: https://doc.wikimedia.org/WikibaseLexeme/master/php/
• Click on "Topics" in the left sidebar

What happens?:

• The url of the page opened is https://doc.wikimedia.org/WikibaseLexeme/master/php/md_docs_2topics_2index.html (note the two "2"s)
• the links to subpages are broken

What should have happened instead?:

• The url should have been https://doc.wikimedia.org/WikibaseLexeme/master/php/md_docs_topics_index.html (no "2"s)
• the links should work

Software version (skip for WMF-hosted wikis like Wikipedia):
Based on the existing docs, it uses Doxygen 1.9.8

Other information (browser name/version, screenshots, etc.):

• Locally, it works as expected with Doxygen 1.9.4
  • However, tests with Doxygen 1.10.0 also show the error, so it might be harder to fix
  • It is still not clear if that is a Upstream Doxygen bug, or an issue with Wikibase Lexeme
• it seems to run the doxygen executable without extra arguments, based on https://gerrit.wikimedia.org/g/integration/config/+/69a52467c2f5b2b75a257c88da6842fcfee75622/dockerfiles/doxygen/run.sh
• In particular, this means that all the links to our official documentation for WikibaseLexeme Lua are now broken everywhere (because https://doc.wikimedia.org/WikibaseLexeme/master/php/md_docs_topics_lua.html is the canonical link in all the on-wiki documentation, announcement emails, etc. Changing that to https://doc.wikimedia.org/WikibaseLexeme/master/php/md_docs_2topics_2lua.html will just mean further breakage once that bug is fixed.)
  • This makes it significantly harder to share that documentation with the respective communities, because either we have to share a broken link or a soon-to-be-broken link