Drupal 7: "Access CiviCRM backend and API Master control" permission Required
This wasn't me, but we had the same issue and fixed it the same way: https://civicrm.stackexchange.com/questions/28085/access-denied-for-specific-role
We have Drupal 7.61 CiviCRM 5.9.0. Whenever a user tries to access the civicrm backend (mysite.com/civicrm) they get an "Access Denied" result. The only permission which fixes this is the "Access CiviCRM backend and API Master control" but it says to give to trusted roles only. This doesn't seem right, but I also don't remember this permission existing before.
I also can't find any documentation related to this permission or what it entails. Interestingly enough, two of the CiviCRM roles already had the permission, but one didn't. And all of these roles were able to access the CiviCRM backend before we upgraded from 4.7.17 to 5.9.1.