Reproduction steps:
1. Open attached project "1341601.zip"
2. Open "SampleScene" Scene
3. Enter Play Mode
4. Notice how the health bars appear above GameObjects in the Scene
5. Exit Play Mode and open the "WorldSpaceUI.cs" script for editing
6. Find row 53 that holds commented out "//container.usageHints = UsageHints.DynamicTransform;" and uncomment it
7. Save the script and enter the Play Mode once again

Expected result: Health bars appear both when UsageHints.DynamicTransform is used and when it's not
Actual result: Health bars only appear when UsageHints.DynamicTransform is not used, and are not visible when using it

Reproducible with: 1.0.0-preview.14 (2020.3.12f1, 2021.1.11f1), 2021.2.0a21 (UI Toolkit is integrated into the editor itself)
Couldn't test with: 2018.4, 2019.4 (UI Toolkit package is not available)