If some entities have the same UUID,the /kill command just can kill one of them.

/summon ArmorStand ~ ~ ~

{UUIDLeast:1000000000000000000L,UUIDMost:1000000000000000001L,}

/entitydata @e

{UUIDLeast:1000000000000000000L,UUIDMost:1000000000000000001L,}

/kill @e[type=!Player]

Found ArmorStand
That entity cannot be found