Note that I found a semi fix here , Edit > Project Settings > Editor settings > Asset Serialization > Mode Mixed > then reimporting the package, the YAML waring have not reapeared. I could Play the Demo, still no Commands on screen, but it seems to work. I can place things and built a structure normally. It also saved the structure, I played again and it was there intact. I have a lot of warning (about 70 ) like this one: The referenced script (ForgeBuilding) on this Behaviour is missing! UnityEngine.Resources:Load(String) uConstruct.Core.PrefabDatabase.PrefabDB:get_instance() (at Assets/uConstruct/Scripts/Core/PrefabManager/PrefabDB.cs:19) uConstruct.Core.Saving.BuildingGroupSaveData:LoadSpecificData(BuildingSaveData) (at Assets/uConstruct/Scripts/Core/Saving/BuildingGroupSaveData.cs:53) uConstruct.Core.Saving.BuildingGroupSaveData:Load(BaseUCSaveData) (at Assets/uConstruct/Scripts/Core/Saving/BuildingGroupSaveData.cs:44) uConstruct.Core.Saving.UCSavingManager:LoadExternalData(Stream) (at Assets/uConstruct/Scripts/Core/Saving/UCSavingManager.cs:191) uConstruct.Core.Saving.UCSavingManager:Load() (at Assets/uConstruct/Scripts/Core/Saving/UCSavingManager.cs:147) uConstruct.Core.Manager.UCCallbacksManager:Start() (at Assets/uConstruct/Scripts/Core/Manager/UCCallbacksManager.cs:102) hope this helps!