When did they start doing this?
Did you make any changes, additions, water changes, any additives or new additives?
Did you change or modify your lighting in any way? Lighting changes alone can sometimes cause polyps to distort.
This is definitely not parasitical.
Testing all of your parameters is where I would start checking.
And believe it or not, all polyps don't have to same skirt appearence, but you said they didn't look this way before right?
Are you running Carbon?
I would consider doing a 20 % water chnage with well aerated water if you are still concerned.
How's your circulation BTW?
Good luck and an update would be great.
Mucho Reef