Torch died with hard bubbles under the skeleton

[eye_dr_reef]

Hello everyone, I lost a healthy torch coral overnight. It started to detach, and after it died, I noticed the skeleton had several hard bubbles under the flesh at the base, forming a fragile crust. All my other corals and fish are fine, and the parameters are stable, but I suspect the same bubbles might be present on my other torch corals.

Has anyone seen this before? Any idea what it could be?

 

[eye_dr_reef]

(P.s.: it’s hard and not spongy!)