Also posted here:
https://www.phpbb.com/community/viewtopic.php?p=14187386#p14187386

On the webiste, if you go to the menu: Customise -> More resources on customising your board » , this link refers to the current page instead of the Customisation page. I guess it is caused by an empty <a href=""> tag.

It happens on the same url as mentioned above (or it seems, anywhere on the community board) and on the blog, but not on the development page for example.