@Kimon Could you please clarify a dedicated (!) URL where users are supposed to report bugs? There are tickets like https://phabricator.wikimedia.org/T335904 but extension maintainers obviously will not find them without a dedicated project tag. If you'd like to use Wikimedia Phabricator for issue tracking, please request a project tag: Phabricator/Creating and renaming projects. Thanks!
Topic on Extension talk:UserPageViewTracker
Considering the low use of this extension, I think using Phabricator is overkill and using this talk page as the main channel for reporting bugs seems enough.