A communication device for handling data transmissions after detecting a failure comprises a storage device for storing instructions and a processing circuit coupled to the storage device. The processing circuit is configured to execute the instructions stored. The instructions comprise receiving a first radio resource control (RRC) message configuring a first data radio bearer (DRB) and configuring a mapping that a first flow is mapped to the first DRB, from a first BS; transmitting a first plurality of protocol data units (PDUs) of the first flow; receiving a PDU of the first flow or a second flow over a second DRB; transmitting a second plurality of PDUs of the first flow; detecting a failure; transmitting a failure recovery request message to the first BS or a second BS; receiving a failure recovery message; and transmitting a third plurality of PDUs of the first flow over the first DRB.