Hello!
There was an issue during the release of 5.5.1 where highly-rated Arena players who transferred could have experienced a partial reset in their matchmaking rating.
This resulted in some players playing multiple matches that would grant them 0 rating for a win (as their MMR had to catch back up). This could take a while, and having to play like this in multiple brackets could become demotivating.
The initial issue was fixed quickly, so it only ended up affecting a very small number of players in this region.
With the latest server reset on Tuesday for this region, we have corrected the matchmaking ratings of affected players to be slightly below their current rating. Of course, players who played enough in the interim to bring their MMR back up to their current rating in a bracket did not receive an adjustment, as they had already corrected it for themselves.
It’s all cleared up now!