Reproduction steps:
1. Open the attached “IN-53933 Dragon Crashers Bug.zip“ project
2. Open the Package Manager window by going to Window > Package Manager
3. In the Packages menu, select the “My Assets” option
4. Select the “UI Toolkit Sample – Dragon Crashers” asset package from the list view
5. Click on the “Import” button
6. In the first warning box, click on the “Import” button
7. In the second warning box, click on the “Install/Upgrade” button
8. In the Import Unity Package window, try collapsing the “Assets” folder two times

Expected result: The “Assets” folder becomes collapsed on the first try and is still visible
Actual result: All of the folders disappeared from the Import Unity Package window on the second try (did not collapse on the first try)

Reproducible with: 2021.3.31f1, 2022.3.10f1, 2023.1.16f1, 2023.2.0b12, 2023.3.0a8

Reproduced on: Windows 11 Pro (22H2)
Not reproduced on: No other environment tested

Workaround (only in 2022.3.10f1 and newer):
1. In the Import Unity Package window, click on the “Next” button
2. In the Import Unity Package window, click on the “Back” button

Notes:
- The workaround makes the disappeared folders visible again but the issue can be reproduced again
- Reproducible in a new project
- The issue only happens when importing the “UI Toolkit Sample – Dragon Crashers” asset package (compatible only with the “2D (URP)” Project Template)
- Could not find any other asset packages from the Asset Store that would reproduce the issue
- Could not reproduce with a newly created custom asset package