Hi I have this issue before and after I update the theme, this issue appears when I try to update a page content or publish or save some content in the site, also we activate the debug in the wp-config file and it show us a problem with the simple twitter plugin so we deactivate this plugin but the problem continues
500 Internal Error says about some issue on the server and can be caused by different things. Anyway, to understand its nature you need to see your server error logs or enable PHP error display on the website. If you can’t do this, you need to contact your hosting provider for help in this question. Here is an article that may help you understand the error better http://www.wpbeginner.com/wp-tutorials/how-to-fix-the-internal-server-error-in-wordpress/
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