Textures flickering in and out

Development Rendering
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1

Is that in game?

2

I get that sort of thing in edit mode, but not in play.

3

What might be the cause of those textures flickering in and out ?

[Giphy Link][1]
[1]: Animated GIF - Find & Share on GIPHY

Thanks!

4

It happens while flying through the level with the free camera AND while playing the game in the editor viewport.