If a spawner with one of the new mobs (illager beast, pillager, etc.) is created, the fire particles coming off of the spawner will build up and not despawn. It does not seem to happen until the spawner charges up for a few spawn cycles (3-6) and will leave particle effects where the spawner is. If the spawner is broken, the particles remain.

-Does not seem to effect previously added mobs.

-If the spawner is changed from the new mob to another, the particles will remain.

-If a spawner with any mob is placed next to the glitched spawner, the particle glitch will spread to all adjacent spawners.

-If the world is unloaded or reloaded, the particles seem to update and disappear.