I cannot find a way to show the red mask when returning to modify an existing selective brush edit. The choices to "auto-show" the mask or hide it seem to do nothing. I am selecting the edit (blue diamond).
If I tap and hold the blue diamond, it will show the mask, but this goes away when not holding which isn't very useful. I have confirmed that I can continue (blindly) making additions or changes to the mask, but I cannot see the red mask while making the changes.
I am using LightRoom mobile 2.8.2 on a 12.9" iPad Pro running iOS 10.3.3.