Increase the max. Nr. of Despooler threads
Out of the Box the Despooler does use three concurrent threads. There may be some situations where the despooler will get overloaded and the backlog of files in the despooler directory is growing...
To increase the concurrent threads, stop the SMS_DESPOOLER component by using the "ConfigMgr Service Manager".
Change the Reg Key:
HKLM\Software\Microsoft\SMS\Components\SMS_DESPOOLER\Despooling Thread Limit = 6 (to increase the concurrent threads to 6).
Start the SMS_DESPOOLER component and monitor the despool.log.