Something has happened on my site where I am unable to add taxonomy terms or edit existing ones.
If I go to add a taxonomy term or edit an existing one the form comes up, I made an changes (i.e. add some text in the description field) and then click save and it goes back to the Taxonomy list but nothing changed. When I go back into edit the taxonomy term the previous change is gone.
The same thing happens when I try to add a term through /admin/structure/taxonomy/name_of_vocabulary/add form- it saves, but then the new term doesn't show up.