How to troubleshoot an Ajax HTTP Result Code 200 Error?` I am receiving the following Ajax error when on any Views page. The Drupal logs (/admin/reports/dblog) don't have any corresponding events. I've tried disabling all custom and view related modules and adjusting jQuery versions with no success.

I'm running Drupal 7.57-dev and Views 7.x-3.18

I know there are several other questions about this error but their solutions are specific or not relevant to this specific response text.

How do I begin drupal shooting this error?
The &lt;?php tag at the beginning of the ResponseText indicates that there is a stray &lt;?php in the markup, this was being caused by a syntax error in a completely unrelated template. 
After template syntax error was fixed the Ajax Http 200 error pop-up went away.