Welcome to the community my friend, I understand your frustration here and I have to give you my respect. Being an admin at the beginning seems fun, but at the end it becomes a job without money . You work your a… so every one will have fun and you gain for payment, criticism and complaints . Still for only a few persons who plays in your server, the effort is worthy . Welcome again to the community
my friend, I really hope your problems will be solved.
I have never had a situation like this
Banned someone for exploiting through multiple foundations used as walls stupid thing to do on his part and cost me some long time players. Have heard of what happened to your server didn’t know how it was done. Being as we are on ps4 I don’t think we have access to server logs or the ability to limit any one potion or anything similar. That might be a Mod on PC . Never used white list have used password but since you don’t know who is doing this that isn’t going to help and passwords can be shared to the wrong person. Wish I had something helpful. When you figure this out I would like to know what you do would be good to learn even if you would prefer to private message. Honestly you might want to wipe the part of your post that explains how it is done so other players don’t use it. Plus forum moderators don’t like cheat methods announced. Good luck to you.
If you and a couple trusted friends start taking players list screen shots you might be able to use a little detective work and lock them up so to speak. If I don’t make a lot of sense woke up saw a message and I am going back to bed good luck again.
. Still for only a few persons who plays in your server, the effort is worthy 
. Welcome again to the community