Steps to reproduce:
1. open ExampleProject
2. open scene "ExampleScene"
3. Press play
4. Open Profiler
5. Choose Memory tab

Result: notice how used memory is increasing.

Reproduced with: 5.5.0a5, 5.4.0f3, 5.3.6p2,
Not reproduced with: 5.2.5f1 (there is no Target Display settings)

Note:
-Adding more Canvas elements or cameras increases used memory growth
-Example Project has 2 cameras (both Target Display settings are different)
-Canvas Render Mode is set to World Space
-You can see creation of the project in a video attached by user (link).