Issue using Print over USB with CURA and Anycubic Mega X

[aprucka 0]

I am attempting to print a file over usb using CURA. The printer connects just fine, and the jog controls all work as expected. However, after the pre print extrusion happens, and the print head moves to the location on the platform where the print should begin, it moves in jolts, extremely slowly, maybe 1/100th of the speed of a normal print. The very same sliced file printed via sd card works just fine. Any idea what the issue may be?

[GregValiant 469]

I think you've discovered one of the reasons why Cura "USB printing" has not been updated in years.  It's flaky at best and prone to random stoppages to boot.  The Octoprint/RaspPI combination is a better solution.

Your specific problem may have to do with your USB cable, the printer USB port, your computer USB port, or the USB to Serial port driver.  Herky jerky movement like that is a hallmark of buffer under-runs as the printer has to wait for the next line of gcode to come in.  Every time it hesitates - the nozzle leaves a blob.