get some blocks and put them underneath the mast channels and tilt forward, get the front wheels off the ground.
run the truck and see if it does it when there is no load on wheels.
try to determine if its a mechanical lock or electrical problem causing the wheel(s) to lock up.
Also when it does this does the display show any errors?
an electrical fault may cause a motor to lock down causing this abrupt stop.

When your driving do you hear anything in the wheel area? like something loose making noise while u drive?
what does the brake pedal feel like when you stop?

it could be some part of brake hardware came loose and is getting wedged in the shoes if it is mechanical.