Disabling mobile tonemapper destroys game preview in UE4.27

Executing console command “r.Mobile.TonemapperFilm 0” spoils the game preview and makes it unusable.

This happens for both Android and iOS previews.

I disable tonemapper on mobile to get more accurate colors and better contrast. But after doing so, I just can’t test my game anymore as a good portion of the screen is blacked out with a kind of Picture-in-Picture (PIP) display. Even the clicks don’t register correctly.

I use New Editor Window (PIE) method to test the game.

This problem was not there in UE4.25, but when I upgraded my project to UE4.27, it suddenly popped up from nowhere.

Any idea why this is happening or how to rectify it guys?

Here’s a snapshot of the problem