This issue has been reported by many players many times prior; however, the most recent thread regarding it was being tended to by Zobrek, who has neither fixed the bug nor replied to the recent activity on the thread, and indeed has not been active in the forums for 19 days.
As of the Imperius patch on 1/8/19, my AI teammates map pool has been restricted to:
Sky Temple --> Battlefield of Eternity --> Volskaya Foundry --> Dragon Shire --> Sky Temple --> …
as a closed sequence that repeats indefinitely. Cancelling a game and remaking it produces the same map until a game on that battlefield has been completed.
This bug has been active with various sequences of four maps more often than it has not since the Hanamura rework back in August. Though it has been fixed temporarily a couple of times, it has often resurfaced with new patches and has been active throughout the entire Toys event. It would be nice if it were remedied soon that we might enjoy some variety while grinding the extension of the event.