Were the 2 that died the ones with Scut on them?
do you have an ammonia test? Check ammonia levels. In fact, check all water parameters and let us know what your tests results are.
No planaria will kill off these parasites, and that can cause a spike in ammonia with all the dead parasites. But that depends on how many of them were in the tank/substrate.
Always do a water change a day after treatment.
If you still have Scut in the tank on your shrimps, a half dose of No Planaria is safer and should still be affective in dealing with parasites. I feel Genchem's dosage recommendation can be a bit too high to be honest. From a product marketing point of view, they want you to use up more than necessary and buy more, but it's not necessarily safe for all shrimps.
Always start with a half dose for anyone else reading.