Tom,
ST01 will give u better picture, look out for Auth ID 'PROJECT_ID' with Return code <> 0 in ST01 which will help you to find why the project does not appear to user/doc type.
Also further make sure the new re assigned 'project_id' is assigned to the respective user roles along with proper auth ''PR_TYPE'' i.e the change doc type. It looks more like a project id not assigned in PFCG the user roles.
Thanks