As the summary says, /call does not respect the vanish API which means players can call someone who is supposed to be "offline" and figure out that they are not.
This can be easily fixed with player.canSee(target)
What if you still want to be able to teleport to the player or request a teleport to the player while invisible? Not every case for invisibility is simply attempting to appear offline.
CMDBOOK-2337 - Reported by Puremin0rez
As the summary says, /call does not respect the vanish API which means players can call someone who is supposed to be "offline" and figure out that they are not.
This can be easily fixed with player.canSee(target)