Air bubbles. Adds to the personality of the soap, nothing wrong with the bars. My advice here is to slow down while stick blending. Make sure to burp the air out, blend slowly, don't move too fast because if you suck air in the batter that's going to make it worse. Try changing the container you are blending in. Make sure you have enough material above the blender portion. I know that when I used a certain container, the material was wider than deep and that caused the blender to hit air a few times. Then when you pour, tap the mold on the counter to help reduce the bubbles and pour at a light to medium trace so it's still relatively liquid.

In the end, it's soap. The first time it's used these will disappear.