How to reproduce:
1. Open the attached project "New Unity Project.zip"
2. Open SampleScene
3. Click Assets > Build Asset Bundles
4. Click Play
5. Observe Console
Expected result: 'loaded Some Object' is printed to the Console
Actual result: 'loaded Some Object' and 'In Rebuild, Could be updating UI' is printed to the Console
Reproducible with: 2019.4.9f1, 2019.4.27f1, 2020.3.10f1, 2021.1.8f1, 2021.2.0a11
Not reproducible with: 2018.4.34f1, 2019.4.8f1, 2021.2.0a12, 2021.2.0a17
Note:
1. When a coroutine continues running after yielding for a web request, it executes in the canvas rebuild loop if there is a synchronous asset load from a bundle of an asset that has a serialized reference to a Texture. This causes canvas rebuild error messages if UI is modified immediately after yield.