If the server spawns an actor and replicates it to you, then your client spawns a proxy. When you walk out of net cull distance the client doesn’t destroy it, then respawn it when you get back in range. It remains in your local proxy world until the server modifies or destroys it. Both would require a replication update (server → client).
Anything disappearing outside net cull distance is tied to either render culling, occlusion or level streaming distance. If you’re using world composition, then assets on the streamed level (tile) are typically bound to the levels streaming distance… as far as I recall. If it’s culled assets bound to it are culled as well.
Also with world comp you have to look at origin rebasing. If the offset gets screwed up then the world position is incorrect. That can lead to disappearing characters/actors.