Edit: After today’s update to 27.0.1, I am getting Mystic Vision again.
iOS 13.3.1 / iPhone 8.
Mystic Vision had been working for me. Occasionally it would say “No ad available”, but I would just quit and relaunch E&P and then one would appear promptly.
Since the update to 27.0.0, it is permanently in “No ad available” status.
I checked storage and freed up 10GB. (wtf Tile app.)
I have tried turning off wifi and relaunching the game with “5Ge” (which is 4G). When I say “relaunch” I mean after a force-close.
I have tried a relaunch of the game while connected to wifi both at work and at home. Before the update I could get Mystic Vision on wifi at both locations.
I tried rebooting the phone and then untoggle/retoggle wifi. (Recommended here.)
I tried Settings -> Privacy -> Limit Ad Tracking -> Toggle on, exit Settings and then go back in and Toggle off. It is off.