So if you generate a world and one of the dungeons spawn a chest next to a mob spawner, it will completely destroy the spawner's blockData and make it impossible to break even with WorldEdit etc and it looks like a pig spawner.

A very very easy way to repo this is to make a world on vanilla 1.14.4 Spigot with the seed -3992479988386776686 and teleport to 2300 11 1694

The spawner will be completely impossible to break and cause issues when interacted with.

My personal stack trace: 

https://pastebin.com/raw/Dmypb1jr