Dear urbanmonkey,

polymer toner can affect the A and B process. But you said that you have no problems, so I don’t think that this is the problem.
In the video you can see how it should work with which settings.
If you are failing with, more or less, the same settings, maybe the toner is causing the problems or, in worst case, the heat press.
If you can upload a short video of your handling and when the problem is appearing, it would be very helpful.