The removal of the textpattern plugin causes a 500 error when loading the page/post edit window. Page content and formatting buttons are also not displayed in the visual editor (though content can still be edited in text mode). When I replace the /wp-content/plugins/tinymce-advanced/mce/textpattern/ folder, the error disappears and the edit window loads as expected.
The error appears below:
GET https://MYDOMAIN.EDU/wp-content/plugins/tinymce-advanced/mce/textpattern/plugin.min.js?wp-mce-4203-20150730 500 (Internal Server Error)