Sometimes I find (a) Llama(s) with (a) lead(s) attached to nothing. With no wandering trader in sight. And I mean none, they are not on an invisibility potion. The lead cannnot be taken but will later vanish completely if Llama is left alone (will not drop it will just disappear). Killing the llama once got me the lead but it doesn’t always happen. The llama regardless of if the lead has vanished or not cannot be leaded by the player. 

If this was as intended it makes no sense that a llama with no lead cannot be leaded