We have some matchmaking enhancements we're going to turn on in unranked today around 3PM PST. This is different than the previous experiment where we changed the max skill rating range. We don't expect any changes to queue times with these enhancements and the vast majority of players actually shouldn't notice much difference.
We identified some cases where the matchmaker was not correctly balancing teams by skill rating. This was rare, less than 5% of matches. But this change drastically reduces this occurrence. This doesn't mean that you will not see players of different tiers in your match. Our change just ensures that both teams have a very similar average skill rating.
If everything goes well, we'll likely turn this on ranked at the start of next season.