Do you have a link to your machine?
On issue is that different machines have different capabilities, so what works on one machine may not work on another.
I ran it previously at 10mm sec. I did not that there were some 'hard stops'/jolts at the higher speed when the cutter changed direction.... Speed to high maybe?
This may be a limitation of your machine. You may be pushing it to hard.
Could it be a laptop issue - app working in the background?
It shouldn't be, because the USB controller should be handling the motion control. But one thing to check is to open Task Manager while the machine is running and monitor CPU usage.