So my question would be, what time of day were these battles? How many other players were in queue? I understand you have been tracking the battles you played but if there are very few people in queue MM will still have a problem matching players onto a team. The same rules apply as in Random battle MM, the MM will attempt to build teams that are more at tier than not and this makes it difficult for MM when there are less players on.
Also, I never said I wasn't looking into this, I was just offering a possible explanation of why this might occur. I have asked our devs to see if anything was changed, however, it is very possible what I said above is true.
Along with the 10 coop battles yesterday, I have already dropped 3 this morning with different tiers and all were full of players.