Reproduction steps:
1. Open the attached “repro_IN-71549“ project
2. Open the “TicTacToe“ Scene
3. Enable the UI Toolkit Event Debugger (Project Settings… → UI Toolkit → Enable Event Debugger)
4. Open the UI Toolkit Event Debugger (Window ->UI Toolkit → Event Debugger)
5. In the dropdown that is in the top left of the UI Toolkit Event Debugger, select “Runtime Panel Settings”
6. Enter the Play Mode
7. Move around (or/and press) the mouse in the Game view until the logged events count (which is displayed in the top left of the UI Toolkit Event Debugger window) is around 150
8. Without exiting the Play Mode, move your mouse on the UI Toolkit Event Debugger and slowly scroll up to the top, then back down to the bottom a few times
9. While scrolling, observe what is displayed in the Event and Target column

Expected result: The information in the Event and Target column is displayed without any errors
Actual result: The information in some lines of the Event and Target column is displayed with errors

Reproduced with: 2023.2.0a18, 2023.2.15f1, 6000.0.0b12
Not reproduced with: 2021.3.36f1, 2022.3.22f1, 2023.2.0a17

Reproducible on: Windows 11 (10.0.22631) (user’s), Windows 10 (22H2)
Not reproducible on: No other environments tested

Notes:

* Since the issue is related to the UI Toolkit Event Debugger, it’s not possible to test it on Player
* Play Mode must be left running when scrolling through the events in the UI Toolkit Event Debugger