You say that you have not changed anything on the machine except the whole transport system …
I would think that your laser head is not at a 90 degree angle and the mirror adjustment is not quite right. The extra frame you get probably comes from the reflection of your laser beam of the inner wall from the nozzle. It will also be the explanation why you can not cut 3mm plywood properly. But, beyond that, look at the tube itself while it is in operation and see what color is inside the tube. Is it white or only very little pink then you need to find yourself a new one. But first try to get your mirror adjustment in place especially no.3 and the nozzle angle itself.
As a side note, I cut 3mm BB-plywood at 750mm / min and 8mA with my 2 year old 40Watt (30-35) no name tube.
