To reproduce:
1. Open attached project;
2. Enter "Main UI" scene;
3. Reimport any Texture or Sprite (Assets > Sprites);
-note: it doesn't have to be a texture used in the scene.
4. Look at the Scene or Game view.

Expected result: UI text does not disappear after reimporting the Texture.
Actual result: UI text disappears from the Scene and Games views after reimporting the Texture.

Note: after changing the size of any (Scene or Game) window or entering Play mode, Text appears again.

Reproduced on versions: 2017.2.0p2, 2017.3.0b10, 2018.1.0a5.
Not reproduced on versions: 2017.2.0p1.