I used to have that problem. It was because I wasn't quilting in quadrants. Your cross lines will turn out better if you start at the center & sew to the edge. Then, break thread & go back to the center & sew from the center to the other edge. Go to the upper right quadrant, starting always on your line that is near center & sewing out to the edge. When you finish, return to dead center & start the next quadrant. That will push the "bubbles" out to the edge rather than trapping it at the intersections.
You want the same spacing for horizontal and vertical lines & generally 4" spacing is the most you would want between lines (horizontal & vertical) if you plan to wash it. I've done less a couple times with my early quilts and the batting bunched & stitches then started coming undone. Also, Heather Thomas (National Quilting Circle) did fabric studies with quilting density & washing. The closer you quilt, the longer it will last. She didn't specify 8-10" lines, but I'd guess mine only survived 20-25 washes before I started having problems. Not worth it for me to put all that time into the quilt top to have it fall apart in 6-12 months. 2" spacing, according to Ms. Thomas, can last 20 years washing once a week & that's probably at least partly due to the cotton fibers breaking down.