How to reproduce:
1. Open the “IN-116799” project
2. In the Hierarchy tab, select UIDocument (1) GameObject

3. In Inspector, disable the UI Document component 

4. Enter the Play Mode

5. Observe the Game window. Notice that letters have usual spacing between them
6. Exit Play Mode
7. In Inspector, enable the UI Document component 

8. Enter the Play Mode

9. Observe the Game window

Expected result: Letters have usual spacing between them
Actual result: Letters are merged with no space in between

Reproducible with: 2023.2.0a5, 6000.0.59f1, 6000.2.7f1, 6000.3.0b4, 6000.4.0a1
Not reproducible with: 2021.3.57f1, 2022.3.67f1, 2023.2.0a4

Reproducible on: macOS 15.3.2 (24D81) (M1 Max)
Not reproducible on: No other environments tested

Note: Reproducible in Player