It may happen that, when trying to upgrade from 11.2 to 12.X, an issue occur with the PWP.
If the PWP switches during the ZDU, the new PWP may face locks on the DB, hence causing the Queues to remain "stopped" (no jobs running).
Error during the ZDU.
Release : 11.2
Component : AUTOMATION ENGINE
Upgrade to 12.X (12.3.3 being the latest release avaialble)