Thanks for the advice, one of the plugins is indeed causing the error. Thank you for your help!
Thanks Rikard. But I would need the Advanced Layout Editor to work first :) It’s in another ticket that I submitted.
On the same note, several other elements under Content Elements and Media Elements do not work. For example, I’m just trying to add an icon list, but nothing happens when I click ‘Add’ at Content Element > Icon List. There must be a common problem to this!