Hi Venkat,
From what I see is the FM IDOC_OUTPUT_INVOIC is a standard FM. So if the fields be missing due to this FM, then it might be the case with other idocs as well. A standard FM cannot be responsible for missing fields of the idocs 
.
There must be some custom ABAP object in the way of the IDocs transaction which is removing those fields.
My suggestion to you will be to please throw more light on what happens when the Idoc flows from its sender to the receiver, or if possible you can figure out a custom object which is involved during the transaction of the idoc and then set up a breakpoint to analyze what has happened.
Kind Regards,
Souvik