Spawning particles at an entity or player no longer works.
/particle lava ~ ~1 ~ 1 1 1 0.5 2 entity @e[type=Chicken]
This only spawns particles at the command block or player that ran the command. The particle command syntax now shows [mode] as the last input. I'm not sure if players are now intended to run an /execute command to spawn particles at an entity or if this is a bug.
Yes. Particles now run off the command block and selectors aren't used.
Run execute @e to make it work.
Duplicate of MC-62638 (Works as Intended)