At present, after running through your recommendations, I’m only running Akismet.
Switching the theme didn’t seem to do anything…
The problem with the admin randomly giving a “Not found” error does seem to have been improved thanks to disabling plugins, so that’s excellent.
But I’m much more concerned about the fact that my site is apparently not showing the updates that I’m making.
Specifically, major page changes that I make aren’t showing up. My Recent Posts widget in the sidebar doesn’t show my four most recent posts. And my top nav menu isn’t displaying the changes I’ve made.
But I can see everything displaying correctly in browsers where I’ve logged into wp-admin and updated my site. That’s the weird thing that’s really stumping me…why can I see the site as updated while nobody else can?