Missing Categories and slow load time for New Post on Wordpress
I just had a weird issue with Wordpress in that everytime I tried to open a new post to write an article the page would hang forever and when it eventually loaded no categories would appear in the list on the right.
The categories were definitley there so I don't know why they weren't loading.
However I went through all my plugins and disabled some and updated others and I stumbled across what seems to the solution.
I had two SEO plugins installed - SEO Ultimate and Yoast SEO for Wordpress.
I liked Yoast for the on-page SEO and Google term searching and I liked SEO Ultimate for the ability to edit .htaccess files and robots files as well as all the other reports (e.g 404) and other features.
However when I disabled SEO Ultimate the page suddenly worked. It loaded quickly and the categories all appeared in the sidebar.
I have no idea if these two SEO plugins were clashing or causing the problems I was experiencing but disabling the SEO Ultimate plugin seemed to fix the problem for me.
So if you have a similar issue and have both SEO plugins installed try disabling one or the other just to see if that fixes it for you as well.