How long have you had them (daisy), have they slowly disappeared or was is a fairly quick thing.
While the pep shrimp won't usually hurt them, you could have a set that does, or what you think are peppermint are actually camel.
it is possible that they pulled at them inadvertantly while gettting other food off your plug.
It may also be a light issue another parasite..........
Your best bet is to keep an eye on the shrimp and see their behavior, I would move the plug to a new location.
Unfortunately there are never any black and white answers to keeping these tanks, just like dogs and kids, same enviroment you never know what you are going to get.