A server-side update has hit Hearthstone Battlegrounds that changes the way the round matchmaking works.

It should be noted that Blizzard originally told us about this update in the Galakrond's Awakening patch notes.

Quote From @PlayHearthstone

A Hearthstone Battlegrounds matchmaking update has just gone live that adjusts the algorithm determining which opponent you face each round.

You will no longer face the same player, or Kel’Thuzad, more than once in every 3 combat rounds (unless there are 2 players remaining).