After changing Canvas background color and entering playmode, canvas contains text "Unknown type: 'Unity.UI.Builder.UnityUIBuilderSelectionMarker'". It also prints this error to the console: "Element 'Unity.UI.Builder.UnityUIBuilderSelectionMarker' is missing a UxmlElementAttribute and has no registered factory method. Please ensure that you have the correct namespace imported."

Repro steps:

1. Open the attached project;
2. Open SampleScene;
3. Enter playmode;
4. Note that there are no errors;
5. Leave playmode;
6. Open UI Builder;
7. Open Assets/UI/MainUI.uxml in it;
8. Click on Canvas;
9. Enable the "Canvas Background" component;
10. Enter playmode;
11. Notice errors.

I've also attached a video to demonstrate the bug.