When the UDM stores the associated Access Type together with the serving AMF as indicated in step 14a, it will cause the UDM to initiate a Nudm_UECM_DeregistrationNotification (see clause 22.214.171.124.2) to the old AMF corresponding to 3GPP access, if one exists. The old AMF removes the MM context of the UE. If the serving NF removal reason indicated by the UDM is Initial Registration, then the old AMF invokes the Namf_EventExposure_Notify service operation towards all the associated SMFs of the UE to notify that the UE is deregistered from old AMF. The SMF shall release the PDU Session(s) on getting this notification.
Step 14d, verbatim
The Old AMF unsubscribes with the UDM for subscription data using Nudm_SDM_unsubscribe.