So when was positional matchmaking sneakily reintroduced to random games?

Just finished a particularly badly matched game a while ago and at the end of the game stats screen, a message pops up saying that the match was tested with positional matchmaking and asked if my position was correctly matched. When was it announced that they are bringing this system back? I deeply disliked the system when it was introduced fully, with matchmaking at its all time worst for a season start, and it just felt like rubbish to see disparate ranks in one game, even if the oh-so-secret MMR ratings may have been level. I sincerely hope that positional matchmaking is not reintroduced.
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