I recently made a blaze farm and the blazes were spawning all well and fine, and when I left and came back to the nether the spawner was not spawning them any more. The light levels are well below 11, it seems there are no other blazes nearby, and the spawning area is unobstructed. I've tried leaving the game and joining again, I've flown away far enough for the chunks to reset, and I can't find out why they are not spawning any more. Also the difficulty is set to easy.