Update: it seems Blizzard have now fixed the bug and the season is back on.

Season 4 (Source)

Our fix for the bug has been tested and deployed. The season has just resumed.

Have a good night!

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Burning Crusade Classic Arena Season 4 abruptly and unexpectedly ended a short while ago, and Blizzard are confirming that it’s a bug and is being looked into.

Season 4 (Source)

Looks like a bug. We’re investigating it.