No se pueden migrar las cargas a S3

Yes, they are in app.yml and I’ve rebuilt the app.
I’ve confirmed that newly uploaded files are going there.

Not quite. I’m using the following environmental variables:

  AWS_REQUEST_CHECKSUM_CALCULATION: WHEN_REQUIRED
  AWS_RESPONSE_CHECKSUM_VALIDATION: WHEN_REQUIRED

Those fixed not being able to upload new files after the settings change.