Hmm. Interesting. I've had these for a short while, they've been doing good an growing until this suddenly happens. Some polyps look totally unaffected though, so I'm not sure what to think.

The first PE polyps I had, I ended up giving away because they just never seemed happy in my tank. The skirts were always folded down and looked a little nasty. I tried moving them all around for light and flow. I finally gave up after a few months, and they were happy as can be in someone else's tank.

Maybe some irritant from another coral in the tank? I recently added yet another leather...