first response all +ve but digital clear blue -ve

we took 3 FR and they showed +ve over a few days, as well as $2 store ones, but a batch of 3 digital clear blues showed as not pregnant (two said it, one was a dud and didn't even show anything on screen)

did we get a bad batch? desperately hoping for a rainbow baby following MMC.

if the fr shows even remaining HCG from the miscarriage then surely the clear blue can't tell if it's old or new HCG?