Various solutions for flexible scheduling of uplink transmissions with respect to user equipment and network apparatus in mobile communications are described. An apparatus may receive a first downlink control information (DCI) scheduling an uplink transmission. The apparatus may receive a second DCI to cancel the uplink transmission. The apparatus may cancel at least a part of the uplink transmission. The first DCI may comprise a first hybrid automatic repeat request (HARQ) process identification (ID). The second DCI may comprise a second HARQ process ID. The second HARQ process ID may be identical to the first HARQ process ID.