Update 7.3 Battlegrounds is live!

[Jerry_the_skunk]

They mentioned in the update notes, that overlaps are possible, especially during the first weeks.

@Jeto

It’s important to note that these groups of players in Leagues are not symmetrical – just because a player is in your group of 30, does not imply you will automatically be in their group of 30. While we are seeding people into Leagues, in the early days of this system, you may find that some players in your group of 30 are actually in a different League to you – this is expected, and should resolve after some time has passed.

Even though this quote makes it sound, like the issue is reserved to different tiers, it seems to be possible inbetween individual ladders as well.