Very slow loading

My blog is running extremely slow. It happened right after editing a post.

I tried disabling all the plugins, switching back to the default theme. -> Still slow.

I installed a fresh copy with no posts or anything in a different directory, had it running just fine and even imported all the posts from the other blog. As soon as I edit a blog post , the entire site becomes impossible to use and goes extremely slow.

Server load, CPU usage, etc., are all fine, as the REST of the site outside of the blog works fine. It’s restricted to WP only.

Any thoughts?