Reproducible with:
1. Open project “UITKTest.zip”
2. Open “SampleScene”
3. Enter Play Mode and observe the label displayed in the top left corner
4. Exit Play Mode
5. Open “RuntimeTheme.tss” and remove “white-space: nowrap;” property from “.unity-label selector”
6. Enter Play Mode

Expected result: no errors are thrown in the Console and the label is displayed in the top left corner
Actual result: IndexOutOfRangeException is thrown in the Console and the label is not displayed

Reproducible with: 2023.2.0a18
Couldn’t test with: 2021.3.26f1, 2022.3.0f1, 2023.1.0b19, 2023.2.0a1 (compiler errors)

Reproducible on: macOS Ventura 13.2.1 (Intel)

Notes:
- This happens only if “Project Settings\Editor\Enter Play Mode Settings\Enter Play Mode Options” is enabled and “Enter Play Mode Settings\Reload Domain“ is disabled
- Also reproducible in Standalone Player