A method of operating a Master gNodeB (MgNB) in a radio access network RAN is disclosed. An indication of a user plane security policy is received from a core network node, wherein the user plane security policy requires user plane integrity protection for a protocol data unit PDU session. Responsive to the user plane security policy requiring user plane integrity protection for the PDU session and responsive to determining that a secondary base station supporting the user plane security policy requiring user plane integrity protection is unavailable, a data radio bearer DRB of the PDU session is established directly between the MgNB and a user equipment UE. Related MgNBs are also discussed.