How to reproduce:
1. Open the user's attached "WebGL Video Bugreport" project
2. Open the Scene "SampleScene"
3. Open the Build Settings (File->Build Settings...)
4. Make sure the "SampleScene" is in the Scenes In Build list and Build And Run the project
5. Once the Build opens press the "Test" button and wait
Expected results: After the first video finishes and waiting for 5 seconds second video starts playing
Actual results: The second video doesn't play, only a black screen is shown (the sounds are still being played)
Reproducible with: 2019.4.20f1, 2020.2.5f1, 2021.1.0b7, 2021.2.0a6
Could not test with: 2018.4.32f1 because the custom Shader breaks