Various solutions for handling out-of-order uplink scheduling with respect to user equipment and network apparatus in mobile communications are described. An apparatus may receive a first control signal scheduling a first uplink transmission. The apparatus may receive a second control signal scheduling a second uplink transmission. The apparatus may determine whether the second uplink transmission is scheduled earlier than the first uplink transmission. The apparatus may drop the first uplink transmission in an event that the second uplink transmission is scheduled earlier than the first uplink transmission.