Thanks, Bob. I don't think that there are any corrupt files because we've played the stuttering/drop-out ones later and they are fine.
We had disabled WIFI, Anti-Virus and everything that wasn't BIAB although it's possible that we missed something so I'll take your suggestion and go through it again.
I talked to PG Music and we returned BIAB to factory settings as you and they suggested - still with no luck.
Geesh!