Drupal 7.56, PHP 5, PHP-FPM, multi-site Ubuntu 14.04.1 LTS server
EDIT: it's NOT only when I'm logged in to my site do I get this error:
Content Encoding Error
The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.
It happens 1/3 of the time I try to load a page. If I click "try again" twice or refresh the page twice it will load. I have followed these steps from the accepted answer on Content encoding error after enabling cache, aggregation and compression
$conf = array( 'cache' => '0', 'preprocess_css' => '0', 'preprocess_js' => '0', 'block_cache' => '0', 'page_compression' => '0', );
I have also checked php.ini, per other resolutions, and error reporting is off.
I checked for PHP error reporting per https://www.drupaleasy.com/quicktips/browser-fail-unsupported-form-compression-related-php-notice and https://www.drupal.org/node/373101 and when I ran the wget command there was no PHP error up top.
The behavior does not change at all after clearing my browser's cache.
FWIW I've tested by disabling every module I could (I'm fighting AddThis right now). I also had to increase the memory limit from 128M to 1000M because I kept getting 500 errors too. See my note on 500 Internal Server Error after logging in
I also had to update a theme.inc file based on this error:
/e modifier is no longer supported, use preg_replace_callback instead in…
UPDATE: the 500 error seems to have been fixed with a permissions reset. I put the memory_limit back to 128M after the permissions reset and no more 500 errors. I got one from Chrome at first but maybe it was a cached thing? Now no more.
Also, per Anson W Han in the comments, I have tried reverting my change to the theme file with no success. And the theme is supposed to be best with PHP 5.2-5.6 and I am running PHP 5.5.9
UPDATE: the 500 error is NOT resolved after all