Out of curiosity, did that affect lower-level matchmaking as well?
It wasn't awful, but my team was historically all Tier IV (the highest rank any of us has achieved is Gold IV--we're all currently Bronze/Silver) and we were put into Tier III against Plats and even a Master.
Unlikely it's the same issue, sorry. This specifically affected matchmaking for the highest mmr folks, and we saw the matchmaking dramatically improve for them on Sunday. Possible something else is going on though.