I also had this issue in morning at 100 KM/Hr after CNG kit service; it was not like this before service, But would see if it continues...strong jerks once/ twice in morning.. there was heavy wind across... any effect bcoz I think this happens when CNG + Air mixture disturbs...
Yesterday, I got my CNG kit serviced (new diaphragm + safety valve), Tuning and Plugs (Bosch WR 78) + Plug cables (NGK) changed.
By the way, just to check prices, I got
Plugs WR78 4-Tip: 250 per piece (forced to by set of 4),
NGK Plug cables: 650.
Rs. 450 for CNG Cylinder oil cleaning, CNG Kit Service, Tuning/Tappets, plugs.