As per release notes, in the current version copying a variety of files to tape medias with “file to tape” job might, indeed, take some time. Though, please be aware that the current implementation is likely to be optimized in the next product versions.
Moreover, you must have been misguided by the any absence of graphical information in the middle of provided “throughput” statistics. It doesn’t mean that VB&R was idling during this period of time, instead, it was copying files of rather small size, so, the processing rate for them wasn’t shown. Once the VB&R had reached relatively big files, the processing rate started to be reflected again.