Just wanted to give an update on this issue:
I was able to solve part of the error by doing what other people suggested in these threads :
In summary, you must release the operation handle used for DownloadDependencies before invoking LoadSceneAsync. That operation handle for DownloadDependencies has a lock on the bundle data until it is properly released.
However, once I added Release to our custom bundle controller, I was still getting the same error, but it would only trigger with the last scene bundle that was required to download.
Our project is setup to download and load several scene bundles after a user selects a scene from the main menu. These scene bundles include the scene the user selected, and other helper scenes that are all loaded in additively. while debugging, I noticed that LoadSceneAsync was being called before the final bundle finished downloading.
This was resolved by adding a yield that waited until all bundles were downloaded and their handles were released. After that change, LoadSceneAsync worked, and our scenes loaded!
I’m not sure why but it seems like the bundles were taking longer to download… either way this thread can be closed.