Do you have any fish in with your cherry shrimp? Most cherry shrimp will stop breeding if they are in a tank with a predatory fish even if the fish is not technically "big" enough to eat the adult shrimp.
I had a thriving colony that would have multiple berried females and the others saddled all the time. I then had to move two of my small juvie wild bettas into the tank (the betta juvies were smaller than an adult cherry shrimp) and the shrimp while still very active and healthy are not spawning at the moment. The only difference is the addition of the betta juvies. I have had the same thing happen when I kept cherry shrimp and scarlet badis (dario dario) together. The shrimp while healthy and otherwise doing great, did not spawn until I removed the scarlet badis from their tank.