Players are shown but are still hidden? (vanished)

I've created a system which involves two players being able to see each other, whilst the rest of the server is vanished, here's the method called to vanish everyone except them:

Code:java

public void vanishPlayers(Player playerOne, Player playerTwo) {
 
        playerOne.showPlayer(playerTwo);
        playerTwo.showPlayer(playerOne);
 
        for(Player players : Bukkit.getOnlinePlayers()) {
            if(!players.getName().equals(playerOne.getName()) && !players.getName().equals(playerTwo.getName())) {
                playerTwo.hidePlayer(players);
            }
            if(!players.getName().equals(playerTwo.getName()) && !players.getName().equals(playerOne.getName())) {
                playerOne.hidePlayer(players);
            }
        }
        //Final check to ensure fighters can see each other
        if(!playerOne.canSee(playerTwo)) {
            playerOne.showPlayer(playerTwo);
        }
        if(!playerTwo.canSee(playerOne)) {
            playerTwo.showPlayer(playerOne);
        }
}

What that does is loops through all online players and vanishes them if they're not one of the two players who need to be shown, and are also not themselves. Afterwards I inserted a check to make sure that both players can see each other.

The problem occurs fairly randomly, every few times perhaps, where one players can see the other but they can't see them, or both can't see each other - something like that. However the strange thing is, I made a debug feature that checks that both players can see each other and will output whether they can or can't, and it says they can - even though they clearly can't.

Any idea on what might be causing this perhaps, or any other plugins that might be doing this?

Thanks a lot.

 

There may be another plugin interfering. Also, players that join later then when this is called will have no effect.