Your mechanic probably damaged the speed sensor wiring. I have seen this many times. The wires get very brittle with age and constant shock movement. You have to be extremely careful when removing caliper not to move it around too much and to place it correctly. I have seen them placing it at the top of the hub while smashing the speed sensor wire and then trying to compress the pads. In your case only to remove rotors since the pads can be changed with the caliper in place. BTW, you always need to bleed them; you should never compress the oil back into the system. This can also cause damage to the system.
Have a tech check your speed sensor resistance while tugging on the wire.