In SPRO, SRM Server - > Cross-Application Basic Settings-->Event and Event Schema for Alert Management-->Define Event Schema
For the PO, check if there is any value for WF_APPR_LATEST_START and WF_COMPL_LATEST_START and clear them.
These values make the workitem go into Waiting status till the configured number of hours have passed.
Please let me know if this helps.
Regards,
Sushil.