I've recently installed this plugin to my server, and I was playing around with door closing.

Putting a lock on double or single iron door, and then trying to open it causes both doors to destroy, and drops the door item twice.

On wooden doors locking a single door causes no problems, but with double doors, the other half of the door gets destroyed (the one not interacted with). And that other half gets dropped twice.

Exploiting this bug, a user could farm inifinite doors.

Try one of the forks.

I created the plugin but I don't maintain it anymore and I haven't for years.