Thank you for your interest in the Herobrine plugin!
Unfortunately, NPCs such as Herobrine need to be displayed in the tab list in order to be visible to players, but it is quite understandable that server admins do not want Herobrine to be visible in the list at all times. To work around this, the plugin uses line-of-sight detection to determine if Herobrine could be visible to a player and if he is, his name will appear in the tab list. This is briefly mentioned on the documentation page for the Herobrine configuration file:
This method works properly for Spigot from which PaperSpigot is developed. This means that if it does not work, then there is a bug with PaperSpigot's implementation and is outside the scope of this plugin. I apologize for the inconvenience.