Separate names with a comma.
Is it a lastest version?
I updated it with your github
It happened before server stop . when a player bought a land "A" before server stop , other players can bought land on land "A" ,and the plugin didn't check if other player had bought the land .And if the server stoped and restarted ,then other players can't bought the land "A" which players had bought . For the plugin check the land now.
It caused by the plugin didn't save the land when players bought the land ,and only save the land when the server stop .So if the server crashed ,the land players had bought may lose .