Photo update as of Saturday, September 28, 2019. This may have been mentioned or posted elsewhere, but I didn't find it. A new building is being constructed behind Pandora's Satu'li Canteen (in the backstage area) and Festival of the Lion King theatre. The building is on the elevated area near the restrooms on the river pathway between Africa and Pandora. This doesn't appear to be a backstage building as there are two distinct roof lines and the façade will be seen from the pathway.
In the below photo, as viewed from the courtyard near Tusker House. The "Lion King" restrooms are in the brown building, with the roof framework of the new building appearing over the top of the restroom building.
In the below photo, as viewed from the courtyard near Tusker House. The "Lion King" restrooms are in the brown building, with the roof framework of the new building appearing over the top of the restroom building.