Still need A LOT more information.
Like what time of day was this? Is it during peak server times? Is it in the AM, evening? What class ship were you playing? When you dropping into queue if you were in a DD, where there 40 DDs in queue and only 4 BBs? Or 1 DD and 30 BBs? All these things play in to MM trying to build a match, because we have it set to try to make the class lay outs of the teams the same. Did you play ONLY tier VIs and then record that? Or did you do Tier IV then V, then VI then VII and only record the VIs?
Beyond knowing all those variables we have always said MM will try to keep uptiering to no more than 40% not it WILL do it, because there are A LOT of variables that go into MM and if you stay in queue for too long, MM will actually override its own rules.
When matching teams, the algorithm also takes your battle history into account, i.e. the number of battles you've played with ships of the same tier as yours and lower, with ships one or two tiers higher, and where all ships were of the same tier. We also collect separate statistics for each battle type and ship tier you play. After a short calibration period, the matchmaker will ensure that the percentage of battles with ships of the specified tier doesn't exceed the set limits, so as to prevent long series of battles fighting against ships of higher tiers. When a player joins the queue for their next battle, the algorithm takes the player's previous 20 battles into account when assembling their team, thus ensuring that the set limitations are met.
That being said, if you're in queue long enough to override the rules you could be uptiered quite often.
-Hapa