Hey. Mojang there its nothing spawning in my world .but my world it's normal in survival.
Try to fix this bug. Probably its the beta or the world.
Check my world its seed (175511341) I have screenshot and I record it.but the spawner its a skeleton spawner.
Thank you for your report!
However, this issue has been closed as a Duplicate of MCPE-38706.
Please add a vote and any new information to the main ticket, which will be updated accordingly.
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