How to reproduce:
1. Open the attached "1299464_Repro" project
2. Open the Scene "SampleScene"
3. Open the Build Settings (File->Build Settings...)
4. Press "Add Open Scenes" button to add the opened Scene to the Scenes in Build list
5. Build And Run
6. Open the Player.Log (C:\User\[User name]\AppData\LocalLow\DefaultCompany\1299464)

Expected results: No errors are in the log file
Actual results: The "Style sheet not found for path "Assets/NewUSSFile.uss" error is in the log file

Reproducible with: 0.9.0-preview, 1.0.0-preview.12 (2020.1.17f1)
Could test with: 0.8.3-preview and below because of the CS1061, CS0426 errors, 0.8.4-preview because I was not able to add a stylesheet to the UXML, 2018.4.31f1 because the UI Builder package was not yet introduced, 2019.4.19f1 because there's no runtime support for UXML Templates, 2020.2.3f1, 2021.1.0b4, 2021.2.0a3 because of the CS0122 and CS0103 errors when UI Toolkit is installed