when you play rafam the legendary that is the result of brood mothers conversion is shown to the opponent. I.E. so you play rafam then you draw your next card lets say it is lore master cho if that lore master cho before the rafam was brood mother then when you draw the cho it will be shown to your opponent.
That sounds very similar to an issue with Bomb cards that are shown to the opponent even after they are transformed by Rafaam. However, that issue is reported as being fixed since April 10: Hotfix Patch Notes – April 10, 2019
Did you encounter this before or after that hotfix? If it is after, then the hotfix may have been targeted towards bombs only and not included other cards that reveal themselves on draw.