this could be a simple case of water getting into the holes where your spark plugs go. It may have seeped into the cavities although the ignition coils are fitted. remove the coils and dry them as well as the holes with air pressure.
This may save you the headache of going to the dealership who may rip you off!
The water is causing a short circuit and the plugs are not firing properly. If the white ceramic part of the plug body has brown colored burn marks, then it might be the case.
Best of luck!
Cheers.