Why do I get a Content Encoding Error?
This turned out to be an unexpected odyssey.


This error was misleading, and actually indicated that some of the page elements were being returned with 0 bytes.
Those elements were civicrm php urls, and most of the errors we noticed where from a 4.7 installation.
There were unhelpful messages in the php error log until I turned on 'catch_workers_output=yes' in the php-fpm.d/www.conf file.
The detailed error 'WARNING: [pool php56u] child 31883 said into stderr: "zend_mm_heap corrupted"' led me to https://bugs.php.net/bug.php?id=65590
A suggestion in that thread "opcache.fast_shutdown=0" appears to have resolved the issue.