In preparation for upgrading the Acquia platform from Ubuntu 12.04 (Precise) to Ubuntu 16.04 (Xenial), we detected that some customers' applications contain an .htaccess file in their applications repo currently located outside the docroot directory. If this is not removed prior to the Xenial upgrade, affected applications will encounter 500 page errors until this file is moved into the docroot directory within the affected application's repo. Any customer with an application that might be impacted by their .htaccess file's location have been contacted by ticket as of 28 April 2017.
To determine if you have an an .htaccess file in your applications repo that is currently located outside the docroot directory, check the path on your application's production environment for the directory just above the docroot by SSHing into your production instance:
Changing to the directory above your docroot:
Then reviewing the list of files located outside your docroot:
Which will return a line that looks similar to this:
-r-xr-x--- 1 www-data [sitename]5.5K Nov 5 2014 .htaccess
You can then remove this file or move it to within your docroot directory via your repository and then push this change to your application's repository via code commit. You can learn more about the Xenial upgrades through our article, "Ubuntu 12.04 LTS (Precise) to Ubuntu 16.04 LTS (Xenial) Upgrade FAQ."