When subscribing to assets via a Steam asset collection screen, users are not prompted to subscribe to required items even if the are defined for the assets being subscribed. To fix, try re-subscribing the missing assets.
assets and then loading a game that was using those assets this can cause the dreaded 'System.NullReferenceException: Object reference not set to an instance of an object' error to appear. Note: Sometimes the error is generated due to unsubscribed building/park/etc. This is most commonly caused by a) asset authors not listing props in the 'Required Items' list on their workshop page or b) end-users not subscribing to props used by an asset.
