Hey, I would first off like to point out, that this issue is NOT for all players, but a good few of the players i've talked to in-game, and on mumble, seem to be having the same problem as me.
Basically, i have a blaze spawner, it's been spawning fine, until around 7pm GMT yesterday (6th may) Where i went offline, and logged back in at 19:30, as i would do, when looking for a new tool, i started to AFK in my spawner, well within detection range, around 21:00, i came back to my computer, to my surprise, I went down my ladder to kill the blazes, and, nope, none, I've been sitting on it all day so far, and still, nothing, I've asked mod's and a member of the development team to come check it out, when they did, it spawned, when they left, it didn't, sometimes people visit my '/home' and when they do, they are within range, some of the people who visit, trigger it to spawn. ZXfear also owns a spawner about 30 blocks from mine, and neither of us trigger each other's, to me, it seems like a bug, where it's somehow not detecting either of us as players, it's pretty disappointing, as a cant ask another player to AFK for me, some of the mods I've asked, seem to not know about the issue, and i haven't seen a post here yet, so i thought I'd just let you know.
Thanks for your time.
-SpikeyThorn