Hammer Coral bubble

[Fink]

I know this question has been asked before, and I did some research on the forums but I couldn't find a definitive answer. My single-head Bi-color hammer has developed a bubble over his mouth. The consensus seems to be that this is either the result of an injury, or the signal of an upcoming split. Most of the threads I found were several years old, so I'm curious whether the community has figured out what that bubble means.

Thanks!

 

[Hydrored]

Upcoming split