How to reproduce:
1. Open the attached project "case1286452.zip"
2. In the top left menu bar go to Edit -> Render streaming -> Download web app
3. In the prompt window select any folder and hit "Select Folder"

Expected result: The prompt window disappears and the downloading of the web app starts
Actual result: The prompt window re-appears without the possibility to close it, the download does not start and a FormatException error appears

Reproducible with: Unity Render Streaming 2.1.1-preview, 2.2.0-preview (2019.4.14f1, 2020.1.13f1 , 2020.2.0b11, 2021.1.0a5)
Not reproducible with: Unity Render Streaming 1.1.1-preview, 2.1.0-preview.2 (2019.4.14f1, 2020.1.13f1 , 2020.2.0b11, 2021.1.0a5)
Could not test with: 2018.4.29f1 (no Unity Render Streaming package)

Note: The prompt window cannot be closed by pressing "Close" or the window "Exit" button. The same error appears when closing.