Update problems

It appears that a rogue extension is corrupting our update site links. For example the correct update site for Flexicontact is:

But some users have reported failures accessing https://www.lesarbresdesign.info/jupdate?product=flexicontact/extension.xml

We don't see this behaviour on any of our sites which is why we suspect a rogue extension. The best solution is to edit the update site (by clicking on the extension name in the Update Sites list). and remove the /extension.xml. Or click the "Rebuild" button to rebuild all the update sites from the extension manifest files. Our extension manifest files have the correct update site location.