Hi Tobias!
Thank you for taking the time to reply,
I grep’d over all the footer.php files in my codebase, and found 2 associated with my themes / plugins. MasterStudy (main theme) loaded it, as did a plugin for masterstudy (MasterStudy LMS – Learning Management System). I disabled the one in the plugin, which seems to have resolved the alert, but I’m double checking it hasn’t affected the site’s functionality.
Have you come across this before?
Best regards,
Miguel