Acro tips breaking off

[jordanrb]

I noticed a few days ago my Westcoast torte acropora got a decent amount of damage within a few hours. It does not seem to be STN or RTN since the actual skeleton is gone. The tips look like they are breaking off and its very randomized. The skin is not receeding when the tips are broken and in the lights off picture you can aee the purple polyps coming through the broken tips. All other acros are fine and parameters are stable. I am trying to figure out if anything could be picking at it.

Ignore the missing area with algae as this is a piece of a colony that was growing on a rock.

I have a clown, firefish, watchamn goby, six line wrasse, gumdrop goby, pistol shrimp squat lobster, harlequin shrimp, pebble crab (leucosia), few cleaner snail varieties and a tuxedo urchin and a few stomatella hichhikers. All from my understanding are reef safe.

I've had this acro for a while, slowly growing and no issues.

 

[exnisstech]

Let's bump this up hoping one of the SPS gurus stops by.
I've experienced similar a couple of times and assumed it was die off for unknown to me reasons. Mine continued to progress.