Just in the past day or so, something has happened to my site.
For some reason, all AJAX calls from Drupal's admin UI are now taking about 50 seconds a piece.
This is absolutely maddening because there are so many areas in Drupal's admin where one field change will result in an ajax callback.
I've been reviewing my network traffic in Chrome Dev Tools and Firebug and see that all pages and site resources are loading at an average of .2 seconds to 1 second.
Then, when I trigger a Form update in the UI, the POST to /system/ajax takes about 50 seconds
The same is true in /ctools/content/ajax/* -- when I am in the Panels screens, AJAX callbacks are averaging around 50 seconds of wait time for the server to respond.
I'm on a shared AN Hosting environment, D7.
I've found that some smaller AJAX requests (particularly those made by Inline Entity Form) do make it through without the delay... I can't see any correlation or pattern between those that do and then those that don't get through. It can't just be one module as I see problems with core Fields UI's and cTools that are totally separate from eachtother
The consistency between failing calls seems to be the size of the POST -- even the basic Field UI has a post size of 252B -- smaller posts seem to not have an issue.