So, if I got this right, it sounds like one of the wheels was doing incorrectly sensing a skid via one of the ABS sensors. In that case, the car would hit the brakes on one or more of the other wheels in order to counteract the skid, which would surely make a Big Noise and make the car jerk around.
I betcha this was a fun one to troubleshoot. The SC is probably fairly familiar with failing drive units. Which, of course, connect to the wheels as well. I can just see it now: a couple-three techs sitting at a table with coffee, open manuals, and baffled looks, arguing about what they're seeing. And one of them goes, "I wonder.. could it be the ABS?" The argument picks up, gets loud, manuals are opened to relatively unused sections, and they all fly off to the car (after finding an open bay), attach test cables and get even more confused.
If I got the explanation correct, the connector was probably in its socket, nice and firm. But, once unplugged and stared at with a skeptical eye, one of the pins was half-way retracted into the connector housing.
Been there, done that, gotten the eyestrain, because four or eight gold-plated pins reflecting off of each other makes life more complicated. Sometimes, using a cell phone in Macro mode, taking a picture, then staring at the picture is the Only Way. Fun.
Glad your car is fixed. And the techies got one to tell other techies about.