Elaine and I conspired ...... 'er conferred about this.
First the bottom puckering is caused by the top thread tension being too loose. I'd also suggest opening up the stitch length a bit.
The walking foot tension may be too tight. Rather than pulling the fabric through in sync with the feed dogs it's pushing it ahead of itself.
There is also a possibility the quilt sandwich is too thick for the distance between the walking foot and bed.
Another thing to do, ( I've done this on my quilted treadle cover ) is to keep the material gently taught with your fingers as it's feeding through the machine.
Joe