One error highlighted by the AtlasPoolMultiTest was an issue with having multiple streams writing an object with the same key. To work around this give the FileMetaData objects unique names by inserting the stream name.
Update all the broken references as a result.
Analysis clients will continue to expect an object called FileMetaData in the output. To support this for now do not add the stream name to the FileMetaData object key for StreamAOD and StreamxAOD. That is a workaround, a proper solution will take more time, this is to quiet the errors.