White bump on goniastrea coral?

[Silverlava]

When I first introduced this goniastrea to the tank, the bottom two polyps struggled, pulling flesh away from the skeleton. I assumed because it was partly shaded at that position. It has since recovered and been growing back. A couple days ago I noticed a white spot between the top two polyps, and I assumed it was skeleton showing. But today at feeding time, it was much bigger, and seems to protrude slightly from the coral.

Photos attached. Any idea what this is?

 

[Reefing Madness]