How to reproduce (estimated):

Open the “Test-Project.zip“ project
Open Edit → Project Settings → Player → Resolution and Presentation
Enable “Run in Background”
Build and run the project
Let the project run for a few seconds/minutes
Switch to another window
Return to the Player
Wait a few seconds
Give any input to the Player (mouse and keyboard) (to ensure that the Player is interacted with)
Observe the Player

Actual results: Player hangs (continues to render animations, but stops responding)
Expected results: Player continues to function as usual

Reproduced locally in: 6000.2.14f1
Not reproduced locally in: 6000.0.0f1
Could not test locally in: 6000.0.63f1, 6000.2.7f2, 6000.2.9f1, 6000.3.0f1, 6000.4.0a5, 6000.5.0a2 (Unable to reproduce after a few initial successful reproductions)

Reproduced by the reporter in: 6000.2.9f1, 6000.3.1f1
Not reproduced by the reporter in: 6000.2.8f1

Reproduced on: Windows 11 Pro (24H2)
Not reproduced on: No other environment tested

Notes:

After a few initial successful reproductions locally, the issue stopped reproducing (the reason is unknown)
The Player hangs without any indication of the reason in the logs
Steps 6-8 might be optional, as the issue had reproduced without them locally. However, after being unable to reproduce the issue, it would be safer to use the reporter's instructions, because the reporter is still experiencing the issue