When configuring a web map in Story Maps (or creating map actions), map image layers are treated as one single layer when setting the visibility as layers. I'm using map image layer a lot in my web maps for several reasons and it's annoying to not be able to toggle visibility of all my layers individually.
What I do now is to create several copies of the web maps with different visibility settings for the map image layers, or adding several copies of the map image layer with different visibility settings in the same web map.
The latter workaround could be used with map actions while the former cannot. But the latter workaround is cumbersome as the map layers need to be configured several times.
