Reproduction steps:
1. Open the attached “BugRepro” project
2. In the Toolbar, open the “Experimental Packages In Use“ dropdown menu
3. In the dropdown menu, select “Show experimental packages“
4. Observe the Package Manager window

Expected result: Package Manager shows the “MockHMD XR Plugin“ package
Actual result: Package Manager does not find any experimental packages and shows an empty list

Reproducible with: 2023.3.0a3, 2023.3.0b3
Not reproducible with: 2021.3.34f1, 2022.3.17f1, 2023.2.6f1, 2023.3.0a2

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

Note: The issue does not reproduce consistently, but restarting the computer or waiting for some time before opening the project helps to reproduce it