sequences that contain around 1MiB of data are dropped from BigQuery export and RetrieveMetadata output currently. 1MiB is not an exact limit, but it can be used as a rough estimate of whether or not the API will drop the tag (this limitation was not documented as of writing this) - we know that some of the instances in IDC will be affected by this limitation. The fix for this limitation is targeted for sometime in 2021, according to the communication with Google Healthcare support.