This has begun happening when we upgraded our projects to 3.5.1 from 3.4.x. In the editor, the screen flashes to white for a second (exact time seems to vary depending on the scene load), and in the build it even shows the desktop.
It appears to happen in all scenes, but within the editor it isn't always visible.
It also appears to happen when opening a scene within the editor (in edit mode).
We have tried keeping the camera alive, removing gui drawing, and disabling all the objects, and found no specific trigger.
WE HAVE SOLVED OUR ISSUE.
One script was wrongly changing quality settings within the Start() function. Specifically, it was changing QualitySettings.antiAliasing = 0;
Even if the AA level was already set to 0 beforehand (in the game config or from the main menu), this caused the game engine to reconfigure the device.
Removing the line above fixed the issue.