Reproduction steps:
1. Open the attached “Repro“ project
2. Open the “Assets/Scenes/SampleScene.unity“ Scene
3. Enter the Play Mode
4. Open the UI Toolkit Debugger window (Window > UI Toolkit > Debugger)
5. Select “Pick Element“ in the top bar of the Debugger window
6. Press on the button in the Game View
7. Expand the Matching Selectors in the Debugger window
8. Hover over the button in the Game View and observe the “Matching Selectors“ list

Expected result: “.unity-button:hover” is present
Actual result: “.unity-button:hover” is missing even though all the other fields represent the pseudo-state change

Reproducible with: 2021.3.38f1, 2022.3.28f1, 6000.0.1f1

Reproducible on: M1 MacOS 14.4.1
Not reproducible on: No other environment tested

Note: Pausing the Game View via shortcut while hovering over the button and then selecting it in its “hover” pseudo-state produces the expected behaviour with the “.unity-button:hover“ is present