If the MES Simplified (Quick) Printing is not working (no output on the desired printer from a workflow or reprint function), the PaperLess.MES.PrintQueueService (which is responsible for background printing), may need to be restarted.  It can be restarted through the Windows Services Panel.   

The log for the service (to help determine the cause), is found under C:\Program Files (x86)\Paper-Less\5.x.0.PaperLess Server\Print Queue Service\PaperLess.MES.Logging.PrintQueue.log or C:\Program Files (x86)\Paper-Less\4.x.0.PaperLess Server\DatabaseSetup\PaperLess.MES.Logging.PrintQueue.log

Note: When adding a new printer, the service should also be restarted, as the service only checks for new printers at startup.