Blast Zone is being received despite owning 4 copies
Using PC, though this is a platform-agnostic bug.
When Fabled Passage was released in M21, Wizards modified the likelihood of receiving one from a pack so that you would only receive up to 4 copies in total (along with the copies from Throne of Eldraine) until you had fully unlocked the rest of the rares in the set.
-I own 4 copies of Blast Zone from War of the Spark
-I've received 3 copies of Blast Zone from Brothers' War
-I only have 1 copy of Underground River and 3 copies of Harbin, Vanguard Advisor
-I would not receive any copies of Blast Zone until having received 4 copies each of Harbin and Underground River