wordpress pages/post slow, hangs and white text

wp version 4.1

I cant figure out what went wrong, didnt change or updated plugins. The only thing i can think of that is different before i had this problem that i inserted 5000 pages with wp_insert_post. (i dont often edit pages).

I insert all those pages as "normale" page.

errors: (half loaded edit page) white text (shown in console chrome) /wp-admin/post.php?post=15195&action=edit Failed to load resource: the server responded with a status of 500 (Internal Server Error) Uncaught ReferenceError: switchEditors is not defined (after clicking text)

whats going on here, anyone idea?