the problem is the devs stated in their tutorial video the EditorDataPath in the preferences options CAN be anything. Actually it only can be
"E:\SteamLibrary\SteamApps\common\Divinity - Original Sin\Data\Editor\" for steam.
as you can see the drive and the steam library does not matters but the "\Data\Editor\ must be exactly this.
Basically the engine stores the mod and its stuff in 3 places
"/Data/Editor/Mods/"
"/Data/Mods/"
"/Data/Public/"
Setting the right editor path will solve this locked terrain editing problem for new mods, for existing ones i am sure you can figure it what to copy where
