Sounds like you have a wheel speed sensor starting to fail. You really need a scanner that shows individual wheel speeds and you will see at low speeds one of the sensors is dropping out and reading 0 mph, causing the ABS to think that the wheel is locked up and activating the ABS. It could also be the steering wheel position sensor failing, but speed sensor is more common for feeling the ABS activating. Either way you need a better scanner to either read wheel speeds or C codes. The scanner that the auto parts stores use for free can only read P codes and ABS and Stablilitrak codes are C or Chassis codes.