To reproduce:

1. Download attached project "2DAdventureGame.zip" and open in Unity
2. Open "Test" scene
3. Click "MapGenerator" game object
4. In Inspector window, in "Map Generator" script you will see "Clear Map" button - press it

Expected Result: All generated Tiles will disappear
Actual Result: Some Tiles will disappear, but not all of them

Notes:
- This issue appears on Windows and OSX
- Workaround: If you will compile project or save it, then Tiles will disappear

Reproduced on Unity 2017.2.0f1 and 2017.3.0b1