Foliage is not an asset that you can select through the World Outliner and the "Select" button in Foliage Tool is not working for this case. If you create new foliage, it will be set to scale 0 and you will have to delete your scene and create a new level for it to work again.
Results: Foliage disappears and can't be re-selected since there is no FoliageActor in the World Outliner
Expected: To be able to re-select the FoliageActor.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-90626 in the post.