How to reproduce:
1. Open the attached project (1327775.zip)
2. Open the Package Manager by going to the menu bar: Window > Package Manager
3. In the top right of the panel press the gear icon and select "Advanced Project Settings"
4. Under "Scoped Registries" add a new one with the following values:
Name: test
URL: https://package.openupm.com
Scope: com.zor
5. Press "Apply" and close the "Project Settings" window
6. Back in the Package Manager in the "Packages" dropdown (right of the plus button, in the top left of the panel) select "My Registries" if such an option exists

Expected result: "My Registries" option exists and packages from the added registry are listed in the Package Manager
Actual result: "My Registries" option doesn't exist or there are no packages listed in the Package Manager

Reproducible with: 2019.1.0a1, 2019.4.28f1, 2020.3.8f1, 2021.1.9f1, 2021.2.0a19
Not reproducible with: 2018.4.35f1

Notes:
1. Reproducible on Ubuntu 18.04 and Windows 10
2. Restarting the Editor loads all available packages