The Yellow Out is using up the chlorine so that's why you get a low FC reading -- that is expected. I would also expect that your Combined Chlorine (CC) reading could be high during this period until you add more chlorine (which will get rid of the CC), but you don't do this right away..

Since you've used this product, I would suggest following its directions which means after the Yellow Out and chlorine addition, wait 24 hours, then add more chlorine again to 10 ppm. That should get rid of any CC.

At that point, you should be back to normal in the pool and can use Ben's chart as a guide and not let the FC get below 3 ppm FC with your 50 ppm CYA.