I have used the AMS Migration tool (https://ams.bitmovin.com/) to serve my content via Bitmovin. The migration is showing up as a success, but the provided playback of my content fails with the error message SOURCE_COULD_NOT_LOAD_MANIFEST.
Most common reason for this is that someone without the required privileges ran the migration. Worth checking if you see the role from the screenshot attached on your media service account? (under Access control (IAM) → Role assignments)
I tried both on the media services resource, and it’s associated storage resource, and that role does not show up as an option to assign.
The media service, and associated storage were created quite some time ago, not sure if that matters.
Storage - appears to be “Storage account (classic)” - so, perhaps some old kind? It does not appear to need the role you describe to function. And my user is an owner on it (and was the user who ran the migration as well)