The shop is correct that it could be from the wheel bearing but it can also be in the wiring to the speed sensor located in the wheel bearing. The reason for it being intermittent if it is the wheel bearing is because the wheel bearing is getting slightly loose and inside the bearing is a tone ring that the speed sensor measures with a very slight gap between the sensor and bearing. If the bearing gets loose the gap widens and sometimes the sensor does not read the tone ring and causes the abs and/or traction control to fail. I've also often seen the wiring harness have the wire break inside and it occasionally loses contact and causes the light to go on for a bad wheel bearing. Unfortunately, without seeing the vehicle I cannot determine which one has failed for sure. A shop can check the wiring harness for resistance on each wire between the speed sensor and the electronic control brake module if the resistance is good while they are moving the wiring harness then the problem has to be in the wheel bearing. Please reply if you have any questions, thanks.