Reproduction steps:
1. Open the attached “IN-100888.zip” project
2. Download the attached “IN-100888_package” package
3. Go to Window > Package Manager and click the + symbol
4. Click “Install package from disk…” and select the downloaded package
5. Open the “MatchmakerBuildingBlock” Scene
6. Enter Play mode
7. Click on the “Enter queue” button
8. Observe the Console

Expected result: No error
Actual result: “Property changed is null” error is shown

Reproducible with: 6000.0.48f1, 6000.1.3f1, 6000.2.0b1
Couldn’t test with: 2022.3.62f1 (Could not downgrade due to errors)

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

Note:
- Does not reproduce if Domain Reload is enabled (in Project Settings > Editor > “When Entering Play mode”) or the UIDocument is enabled only during Play mode