Steps to reproduce:

1. Open attached project "850240.zip"
2. Open scene "test"
3. In game view, set display to "Display 2"
4. Run scene and notice that button isn't clickable

Additional steps:
5. Exit play mode and in hierarchy select "Canvas"
6. Switch to "Screen Space - Overlay" and set Target Display to Display 1
7. Set Canvas back to "Scree Space - Camera" and run the scene
8. Notice that this time button interacts with mouse input

Reproduced with: 5.4.1p2, 5.4.2p4, 5.5.0b11, 5.6.0a2
Not reproducible: 5.4.1p1
Regression introduced in: 5.4.1p2