Ref: Distinction between [facebook-chat] and [facebook-messenger]
The A there includes:
I don't think there is a distinction. I think the former should be a synonym of the latter.
It has been upvoted and not downvoted and has been up for over a month.
It is impractical to retag (121 instances) and very few users are eligible even to make/support the synonym suggestion.
Possibly the tag wiki should be transferred.