Only tutorial i that used the mannequin for particles was using niagara and seems to be broken 
You have an entire level with an example of Niagara + skeletal mesh effect in the map called Niagara at the Content Examples project found at your Epic Launchers’ Learn Tab. Just opened the version 4.21 and works ok!
for some reason i never noticed that learn tab! thanks a lot 
ill watch through some stuff and share what i came up with