Are you preventing the bots from reaching the exit at all by having no remaining paths they can take that dont have an avoid? If so, bots will ignore the avoid and continue anyway. They always need 1 valid path.
The only effective way to block them without ever letting them through is a respawnroom visualizer, this actualy behaves as a wall and realy denies them from walking further. And yes, they can be enabled/disabled although you must refresh the nav at runtime (yes, there is an entity that can refresh nav info, look in rottenburg for an example as thats how the barricade is made).