When I use a command to give me a custom mob_spawner, and place manually the block to start the mob generation, it generate one of them, and turn itself into a pig spawner just after.
/give @p mob_spawner 1 0 {BlockEntityTag:{SpawnData:{id:"minecraft:spider"}}}
If I use a setblock command to place the spawner directly, the issue does not occurs. For now i use setblock command as a workaround.
I Saw a lot of issues talking about mob_spawner turned into pig spawner, but not about a spawners doing it right after the first generation.
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[media][media]
Dupe of MC-92282