Including Drush in an Acquia Cloud application branch may disable some Cloud Drush commands, notably Install distribution which allows you to install a different version of Drupal into the deployed branch.
The suggested workaround is to remove Drush from the branch in which you wish to install a Drupal distribution. This can be accomplished by modifying an existing branch or creating a new branch without the existing application's code.
Drush is generally found in one of the following directories:
Usually this is done with Composer; if so, Composer should be used to remove Drush as follows:
$ composer remove drush/drush
The root cause is that Drush detects a version of Drush installed in an Acquia Cloud application's code and switches to run in that context.
Acquia Drush commands, like
Install distribution, are not currently available to “vendored” Drush, disabling some features. Acquia is preparing a solution to this issue.