BG has not allowed it since 2006, when it was explicitly prohibited. Under 18s were not allowed to share rooms with over 18s. But it certainly was not common practice for adult male coaches to share rooms with teenage female gymnasts.There is an article summarise the documentary Here (paywalled).
heads should roll at BG merely for allowing adult coaches to share rooms with young gymnasts. Such a glaringly obvious failure to apply any basic safeguarding measures.
I remember it clearly, I was 16 at the time, training and coaching in Surrey. It was not a popular rule, and was met with a lot of sighing and eye rolling. It was fine for me to share a room with the 8 year olds I coached, but not with the 18 year olds I trained with.