Check the PCB
This issue is likely caused by noise coming from the PCB box. Try to remove the PCB control box from the machine. Make sure that none of the cables are touching any ports or the processor on the board. Try to run the machine with the box away from the machine, and if the issue doesn’t crop up again you know that the wires were getting noise off whatever they might have been touching.
Be very careful when replacing the PCB control box to ensure that no cables touch the ports or the processor. Many users will zip-tie the cables to keep them away from these parts with success.
Where applicable unplug the rear handlebars and check to see if the front handlebars work independently. If they do there is an issue with the rear handlebars.
Where applicable unplug the front handlebars and check to see if the rear handlebars work independently. If they do there is an issue with the front handlebars.