A first access and mobility management function (AMF) in a network receives, from user equipment (UE), a registration request listing a first network slice and a second network slice. Upon determining that the first AMF supports the first, but not the second, network slice, the first AMF causes selection of (i) the first AMF as a session and mobility management (SM)-AMF to perform mobility management, and first session management signaling for the first network slice; and (ii) a second AMF as a session management only (SO)-AMF to perform only second session management signaling for the second network slice. The first AMF, acting as SM-AMF, performs the first session management signaling for a first data session on the first network slice, while the second AMF, acting as SO-AMF, performs only the second session management signaling for a second data session on the second network slice.