Seems you are using deprecated theme version (you have old styles in admin panel), please check http://prntscr.com/kli7em.
You need to update the theme up to the latest version. Please check this article for more detailed information.
I’m really sorry to bother again. I’ve updated the theme according to the link. After uploading the zip file, the site seemed to be working fine. I then uploaded the backup file .json and now I’m back to the faulty map display. What do I have to change in order to not overwrite the API?