Adding and removing favorites sometimes fails

Version 1.4.0 of Favorites Application does not work on version 16.10.9.
When I try to add a page to favorites, from the More action menu, there is a pop up window down the page saying "Hello world".
If I try to add a page to favorites through the profile page (Manage favorites) it fails, but without any errors what so ever.

Version 1.4.0 works ok on XWiki version 15.10.15.
Version 1.3.9 works ok on XWiki version 16.10.9.