How to reproduce:
1. Open the user's attached project
2. In the Project window, navigate to Assets/Scripts/Runtime
3. Right-click any of the folders and/or select multiple
4. Select "Reimport"
5. Repeat the reimport up to 30 times while selecting different folders

Expected result: an additional Editor window does not open
Actual result: an additional Editor window opens

Reproducible with: 2020.3.17f1, 2020.3.33f1, 2021.2.17f1, 2022.2.0a9
Not reproducible with: 2020.3.16f1
Could not test with: 2019.4.36f1 (Script errors), 2021.1.0a1, 2021.2.0a1, 2022.1.0a1 (Package errors), 2021.2.15f1, 2022.1.0b15 (Unable to resolve reference 'System.Private.Uri')

Notes:
1. On Windows, the new Editor instance is unresponsive
2. On Windows, the reproduction takes fewer attempts and is more consistent than on Mac
3. On Windows, sometimes two unresponsive Editor instances open, but shortly close
4. On Mac, the issue takes fewer reimport attempts to reproduce if the project is unzipped and opened anew, while it takes more attempts if the project is opened for the second time
5. On Mac, the TMP Importer window opens on 2020.3.17f1, while from 2020.3.19f1 onward the window is blank but of the same size; from 2020.3.31f1 it is the TMP Importer window again
6. In some versions, the error "Unable to resolve reference 'System.Private.Uri'" prevents reproduction
7. Circumstances of the reproduction vary from machine to machine on the same OS