It's probably got a wheel brake deactivated because of a fault, which is allowed in the 787 Dispatch Deviations Guide (DDG)
From the 787 DDG:-
Wheel Brakes may be inoperative on one main landing gear wheel per truck provided (amongst other things) the inoperative brake is deactivated and after takeoff, the gear remains down for two minutes before retraction.
As part of the normal retraction sequence, the wheel brakes are applied to stop the wheels spinning before they enter the gear bay. If a brake is deactivated, the affected wheel cannot be braked so the gear is left down for 2 minutes to ensure the wheel has stopped spinning
FF