When I activate a Layer State, Rhino is turning off the Model On setting for layers which are not selected by the Layer State. In order to activate other layers manually after activating a Layer State, I have to activate each impacted layer, then reactivate the Model On setting. This is new behaviour. There does not appear to be a Model On setting in the Layer State scope settings, so I cannot think of anything that I might have accidentally changed.
@Japhy After activating a Layer State, try to activate the layers which have been turned off by the Layer State. The layers show as active, but their objects do not display until you also activate Model On.