So I would first examine the bleed valve for the clutch actuator at the bottom front of the engine. Maybe you have minute seepage that is not apparent as a sudden loss of fluid. You may have been slowly losing it over time.

You're going to have to remove the front lower cowl and the evap canister to get to it.

Then, if nothing apparent refill the master clutch cylinder and flush the entire circuit. Then monitor it for loss of fluid.