In 5GS, Single-Network Slice Selection Assistance Information (S-NSSAI) based backoff (BO) timers (T3584/T3585) can be applied to either the registered PLMN or all the PLMNs based on a 5GSM congestion re-attempt indicator. For a specific PDU session, the corresponding BO timer applied to the registered PLMN and the BO timer applied to all PLMN can be both running concurrently. It is proposed for a UE to stop both the BO timer applied to all the PLMNs and the BO timer applied to the registered PLMN, if running, in all the following scenarios: 1) Receiving a PDU session release command without a BO timer, 2) Receiving a PDU session release command with 5GSM cause #39, 3) Receiving a PDU session modification command, 4) Receiving a 5GSM message with a 5GSM congestion control BO timer value, and 5) Receiving a PDU session authentication command.