My installation was working fine a few days ago.
For some reason now whenever I try to choose a category for a post, after clicking save the categories are not added to the post.
If I save a post and try to add a category to it afterward, it still doesn't save.
I turned on debug mode and there are no errors coming up.
If I simply add in a row in the wp_term_relationships table with object_id as the post and term_taxonomy_id as the category id, the category is added fine.
What is causing this? My client can't use the installation. I've tried everything, including updating wordpress. I've searched online for a really long time and I can't find anything.