We found a workaround for this.
In the directory
C:\Users\[name]\Documents\Larian Studios\Divinity Original Sin\PlayerProfiles\[name]\Savegames\[savegame]\LevelCache
we deleted the file LucullaForest.lsb
After doing so the game let us progress to the next area, except that our map discovery for Luculla Forest had been reset. Just the map though, quests and NPCs seem to still be in order.
