My thought, too.

I had a similar problem a while back. I finally figured out that I had different weights of thread on the top and the bobbin. I made two similar tops in a row and only had problems with the second one. My conclusion was the thread difference.

bkay

Maybe try a presser foot adjustment to prevent the bunching up of fabric that may be causing your seams to pucker.

https://www.thespruce.com/presser-foot-pressure-2978303

There was just a whole discussion on this board regarding this type of adjustment.

Thanks everyone for wonderful tips. I plan to try them all and find one that works. I don't even know if my machine has a pressure foot pressure adjustment and it's only 6:42 AM so too early to call the Pfaff dealer. For those of you who asked, I am cutting my own logs, and using Aurifil 100% cotton thread top and bottom, with the IDT (walking foot) engaged. Thanks for all your help.

I could be mistaken, but I think I have that same model of Pfaff. Push the "tools" button. (It is a toggle button.) There you find the pressure for the foot. I always decrease mine by only one increment. You have to push the "tools" button again to get back to your main menu.