excuse the weird PM...too early for me! hope your machine decides to work better this morning. I'm still thinking thru the problem...with the bottom not moving thru and the top moving thru (with batting) it sounds like a feed dog problem...the thickness of the batting making the difference. It's possible something happened between the runner and this placemat but I'm not the one to determine what. This discrepancy would also cause the puckering.
I normally suggest that a person not touch their bobbin tension, but in this case, did you try adjusting it? Not sure why it would suddenly tighten up on you tho...so again, I'm cautious about changing it.
I occasionally get a similar problem when at the beginning of a seam one of my thread tails gets caught up in the seam or in the bobbin case...did that happen by any chance? I try to hold them when I start a seam but sometimes get too busy to remember and that's when it happens.