1. Download and open user's attached project 'CanvasTest.zip'
2. Open the Scene called "Loading"
3. Find Black50% Image and set its alpha to 255 to be fully opaque
4. While Unity is Playing if you Disable and Enable the TemplateCanvas it draws incorrectly, the Blue rectangle(Sort Order 3) sorts over the Black50% rectangle(Sort Order 100)
5. If you then change the Sort Order of TemplateCanvas to any negative value and back to 0, it fixes the sorting order.

Actual result: The Blue rectangle sorts over the Black50% rectangle.
Expected result: The Blue rectangle doesn't sort over the Black50% rectangle which has a higher sorting order value

Reproducible with: 2017.4.17f1, 2018.3.1f1, 2019.1.0a13

Note: If you move the Blue GameObject so it's a child of Content instead of Yellow(Override Sorting -> Sort Order 1) and then Play the scene it draws correctly.