In a recent SDK update, the Scene Descriptor doesn't show the Network IDs list, making it quite difficult to manually tweak Network IDs.
I believe this is unintentional as the Editor component for the Scene Descriptor still has code to build the inspector for the Network ID list.
The problem is with the line
propNetworkIDs = serializedObject.FindProperty(nameof(VRCSceneDescriptor.NetworkIDCollection));
because "NetworkIDCollection" is not the name of the serialized property for network IDs. The correct name is "NetworkIDs".