People not actually being available for invite

I've had a problem were a certain person on my friend's list is always visually not in a game, and is available for an invite, but when i mass invite to try and fill up a team builder it says that they are in a game. I messaged the person and asked them, and they were, in fact in a game. This has happened with this friend for about a week now, and I've only seen it on a different friend once.