George Russell stopped his W14 in the afternoon session of the second day of testing. His steering wheel indicated a hydraulic failure. For Mercedes, this seems to bring the second day of testing to an early end.
The hydraulic problem might not be very serious straight away, it could also be a broken sensor that needs to be replaced. In any case, Russell and Mercedes are missing out on precious time on the asphalt. However, if it is a sensor, they could reset it quickly and then have only lost out on nearly as much track time as everyone else.