Hi REBI SRM,
Ethe issue got resolved as I ran the FM BBP_PD_SC_TRANSFER. After this the follow on document are created. The issue probably poped up because the cart creator opened the cart in edit mode after 4-5 mins the cart was cerated, so the system might have tried to update the cart at the same time but failed to do so(found this in BBP_PD).
Also, there is only one approval for this cart and that too is auto approved by the system.
Thanks for your help.