Only time I experienced that, it’s because the 3 wire PWM cable going from the receiver to the ESC was smashed (between the ESC and enclosure which were bolted together) and the signal wire was almost completely broken.
That’s not the low battery behaviour — UNLESS you didn’t set the failsafe, then it could be. If you turn the board upside down while on, then turn off the remote, do the wheels stop turning?