Hello Harsh,
Once, you are on the PO main screen, click on Messages. The output are displayed, from there, in the main menu, click on Goto and select "Determin. analysis".
This is the starting point for your investigation. The log displays per output type which conditions are triggered or ignored or found but not executed...
Additionally, I already came across an issue where an output with a custom condition table was not triggered in some situations and I had to move it up in the sequence sequence. This is managed under MM>Purchasing>Messages>Output Control :
Analyse the PO messages log, check your system configuration to determine how the settings are influencing the output control for the problematic message type.
Alexandre