Confirmed on Windows 10 1.17.34.
Steps to Reproduce:
- Download the attached file
- Extract the contents (one folder) and move it to the com.mojang\minecraftWorlds folder in your Minecraft AppData folder.
- Restart Minecraft to cause the world to appear in the Worlds screen
- Open the world. Observe that the spawner is spawning skeletons.
- Go through the Nether portal, then return.
Observed Results: The spawner stops spawning new skeletons.
Expected Results: The spawner continues functioning normally.
I tried several ways to make the spawner resume functioning.
- Reloading the world fixes the problem.
- Changing /gamerule mobspawning (false, then back to true) has no effect.
- Changing /difficulty (Peaceful, then back to Hard}} has no effect.
- Teleporting or flying away far enough to stop ticking at the spawner doesn't fix the problem. (Although I think this contradicts what some other people have said, I was not able to get the spawner to resume functioning by flying or teleporting away and back.)
Also, the issue is with the spawner block data, not just in the code. Once you have a spawner that has stopped working, you can place a second spawner a few blocks away, put a spawn egg in it, and it immediately starts spawning mobs.
Thanks to UnShippedMod for the sample world!