This error means that “override” does nothing and is never loaded. It was probably doing nothing before when your mod was working it’s just that the game was not reporting the errors about unvisited members. Just remove that entry and you should be good.
If you used “override”: true to signify that this should override the vanilla item with the same id you should probably replace it with "copy_from": "hdhatch_opaque"
That comes from my misunderstanding what override did.
I thought with that entry it meant the vanilla item values were all ignored for whatever I placed in the custom entry. With using “copy_from” allowing you to change select parts.