Steps to reproduce:
1. Open the attached project(Equilibrium of Divinity.zip)
2. Open the Assets/MainMenu.unity scene
3. Play the Scene
4. Load save slot 2
5. Find an enemy (use W,S,A,D to move)
6. In the battle select a spell, hover over an enemy but does not use the selected spell
7. Select a spell again, hover over the selected spell level and right after try to select an enemy (which is not visible)
8. Observe, the green square will disappear as Canvas(Canvas Tooltip (New2)) stops rendering

Expected result: Canvas should render normally
Actual result: Canvas stops rendering

Notes:
Unable to test with 5.3 and 5.4
Unable to reproduce with a new project
Log file has reported:
d3d11: failed to create vertex buffer of size, d3d11: attempt to lock null vertex buffer (with Windows 7 and Windows 8.1)
Log file has reported:
d3d11: failed to create vertex buffer of size 7392
d3d11: failed to create index buffer of size 744
Assertion failed on expression: 'SUCCEEDED(hr)'
(Filename: C:\buildslave\unity\build\Runtime/GfxDevice/d3d11/D3D11Window.cpp Line: 214)
Assertion failed on expression: 'SUCCEEDED(hr)' (Windows 10)
With Windows 10 Unity crashes/freezes
When you hover over an enemy the Tooltip Container is moved to Canvas Tooltip (New2)
When you hover over a spell level the Tooltip Container is moved to CanvasMain

Reproduced with: 5.5.0f3, 5.5.1f1, 5.5.1p4, 5.6.0b9