I have added blueprint nodes to create a spline mesh in the standard Third Person template. I am using the AddSplineMeshComponent node and setting the static mesh. Very basic stuff. The spline is created fine for the server player, but when I run in multiplayer the client is not able to create his own spline.
I have tried creating these splines both local and with server side code, but I get the same results either way. Note that in my case, the splines should only be seen by the player that creates them. It is not necessary to replicate them to other players.
I am using UE 4.91. To duplicate this, just create a spline on a button click in your controller, then run in multiplayer. Notice that the client does not create the spline.