Recently in my new Minecraft world I've been caving and finding some peculiar monster spawners. The cage and flame particles are all there, but there is no monster inside of the cage, and no mobs spawn out of it. If anybody has a fix for this, please answer. Also, I would rather not restart on a new world, as I've already put numerous hours into this one. Also, the glitched spawners were not only in this one mineshaft. There were spawners like this in other caves too. I am currently playing on normal difficulty, and other mobs spawn normally
From my research in Mojang's Bug Database, I have determined that your empty spawners are bugs. Some links which include reports about the bugs are listed.
Each of these bugs occured in Minecraft Pocket Edition.
These links elaborate and prove that this is a bug.
Please tell me if you are not using Minecraft Pocket Edition, and I will do more research.