Could you perhaps explain what area of the pool that is and what we are looking at in the photo? Is that the drain in the spa?
I agree with
@ajw22 - those look like superficial shrinkage cracks that occur when the plaster initially cures. They are not structurally significant.
And what do you mean by “air bubbles” occasionally coming from that area? Are they coming from the crack itself? From the plastic grating?
Also, please fill out your signature line with your equipment and pool specs. It makes it harder to help when there’s no information about the pool.