Wiki advanced editing extremely slow. Now throwing a 404 error

The pages on the front end of my site load fine, but when I clicked the advanced tab in the past to edit a wiki page it sometimes took up to 30 seconds for the admin section to load that will allow me to edit the page.

Today I clicked the advanced tab and the site is throwing a 404 error instead of bringing me (slowly) to the advanced editor page.

I am able to edit (quickly) using the edit tab just fine.

Any ideas? My dashboard for my site is up and running, but anything having to do with the wiki on the backend is extremely slow and as mentioned above, throwing the error listed above.