LoadAsync on ArcGISMapImageSublayer should not have any effect on how ArcGISMapImageLayer is rendered, it only retrieves metadata. Are you by any chance rendering the sublayer as FeatureLayer?
Can you share some repro code? Thanks.
You can subscribe to GeoView.LayerViewStateChanged to find the current status of the layer when it becomes invisible, see if LayerViewStatus is OutOfScale, NotVisible or if there's an error associated with it.