Yes, this has happened to me before. I was doing the exact same fate, I had tagged a mob, then went and un-synced after I had finished enough to get gold. And after the person had killed the mob I tagged, it had told me "Unable to Obtain item. You are too far above the recommended level for this FATE." So, my guess is probably same thing happened to you, you might have accidentally tagged a mob enough to get the item to drop off it, but since you're un-synced you can't obtain it.