I've created a Drupal site which behaves rather strange - whenever I click an item in the administration menu or use a contextual link to edit a page, the half-opaque overlay shows, but no editing window opens on top of it as it should (not just "not immediately", but never).
Once I'm in "overlay mode", if I click a menu item, the linked page opens as it should, on top of the overlay. From here, all items work as intended, except when opened in a new tab - that will also only show an empty overlay page.
When the overlay is eventually closed again (for example, by clicking the home link to return to the front page), the error described above will reoccur the next time an administrative link is clicked.
Can anyone assist me in finding the source of this problem? Please let me know if you need additional information.
The site was built on 7.53 originally and is now updated to 7.54 (up to date). No changes to the .htaccess file have been made, therefore all of my changes are within the /sites/ directory.
I'm using these contrib modules: Chaos tools, CKEditor, Views, Views UI, Webform
My administration theme is Seven.
I've set up other Drupal 7 sites on the same environment and didn't have this problem, so I clearly I did something different here. I have no idea where to start looking, though, and wasn't successful in finding other questions or external info covering anything even remotely related.
