Error while rendering template [htmlheader.vm] when clicking on 'Forgot your username' and 'Forgot your password' making the templates unreachable

This issue doesn't seem to consistently reproduce, in particular not in upgraded production instances like myxwiki.org (no idea what the criteria for reproducing the issue is, though). However, I was able to reproduce the issue in a fresh demo instance launched using xtool, so this should be reproducible with a clean demo instance. On the chat, Nikita also reproduced it with a fresh demo instance on Windows.