Peppermint shrimp have strange habits. Had 3 in our tank, 2 got eaten by the pistol shrimp, the remaining peppermint had to be taken out after it terrorized a frogspawn, stole & ate a ricordia, and killed an scan.
Good luck getting yours out of the tank, they are tricky to catch.
Had a pair of peps and when I added a frogspawn one of them immediately began to dice it up; it took me about an hour and tearing all my rock work apart to catch the little buggers. No more peps for me, love my skunk cleaner!