UnityWebRequest cookie cache rolls back to an older value when a slow concurrent request completes without a Set-Cookie header

How to reproduce:

1. Open the attached “IN-152325“ project
2. Open a Terminal in the project directory
3. In the Terminal, run this command: py tools/server.py to start the test server
4. In the Editor, enter Play mode
5. In the Tools menu, run the CookieRollbackTest (Tools > CookieRollbackTest > Run test)
6. Observe the console

Actual result: The Console shows “actually received: v1”
Expected result: The Console shows “actually received: v6”

Reproducible with: 6000.0.0f1, 6000.0.83f1, 6000.3.23f1, 6000.5.11f1, 6000.6.0f1, 6000.7.0a6

Reproducible on: Windows 11
Not reproducible on: No other environments tested

Notes:

• Reproduces in the Player
• Requires Python 3.x to reproduce the issue
• Server logs are located in 'Project Directory/tools/server.log'