The only shrimp that my clowns ate was the sexy shrimp. They are cute little shrimp and clowns have a hay day with them. Don't put these into your tank.
I have never heard of clowns eating a peppermint shrimp though. As suggested do look to see if it was not their molt they were eating and the shrimp might be hiding for a few days.
What kind of clowns are they?
What other fish are in this tank?
Deb....