When user prints and you don't see anything in the Job list and at the same time you see this error in the Web log:
WARN|||OptimiDoc.Web.Controllers.BaseController|Print job from unknown user John Doe was rejected.
Solution of this error should be simple as you just need to assign that "John Doe" login, which Windows sends along with the job, to the already existing user or create a new one, you can do so in the section Diagnostic / Unauthorized accesses, find the record in the list and click on the button based on the action needed. It is usually the case of computer which is not in the domain hence we don't recognize the user name/login.