One issue I see a lot when working on client systems is the: ERR_EMPTY_RESPONSE error in the browser. Searching Google, you can see this is a very common issue but very rarely is there a common way to resolve this issue. This is my solution to fix the ERR_EMPTY_RESPONSE error for WordPress. This solution has worked for over 90% of the systems I have managed.
Note: this solution may not solve your problem and it is not the absolute fix for this error but it is one that seems to be very common on systems that are not properly managed. Your typical WordPress response to fix an issue is to go down a long list to basically get your site back to a vanilla state of WordPress then install and activate everything one at a time until you can duplicate the issue. While this way tends to work, it is not ideal and can/will give you many false positives. My suggestion is to try this step before you go through that hassle.
The issue I have noticed is due to a PHP settings that is almost always setup improperly. The setting I am referring to is: output_buffering
I have seen the output_buffering value set as high as the server memory… A tell-tale way to identify if this is your issue is seeing: zend_mm_heap corrupted in your error log. This is typically in your main error log for Apache and not your virtualhost error log.
What you want to do is set this to a value that makes sense for your environment setup. It should be noted that this value is bytes. I mostly see a value of 4096 and this works for some but not all environments. Some system I have had to set to 1024 for it to prevent the ERR_EMPTY_RESPONSE error.
Again, this is not an all-mighty fix all but it is something worth checking before you go down the WordPress rabbit hole of finding the plugin that caused it. Mostly because an issue like this would not be identified by doing that normal process in the first place. This simple check has saved me numerous hours of work. Hopefully it will help you too.
