Some of Minyaa Workflow-Function (Condition, Validator or Post-Funciton) retrieve the Remote User using the webwork.action.ActionContext.getSession().get(DefaultAuthenticator.LOGGED_IN_KEY).
With the Auto-Transition service, it causes a NPE since the User is not known in the Session.

The Remote User has to be retrieved using com.atlassian.jira.component.ComponentAccessor.getJiraAuthenticationContext().getUser();

An improvement for MYAA-1447 will have to be done in order to support any user account in the Auto-Transition service.