Hello,
I was working with electric data and encountered a somewhat same error message.
ERROR 000224: Cannot insert features
ERROR 000224: Cannot insert features - The value of the subtype code is NULL. [ (class name: XXXX_TerminalTest.UNOWNER.ElectricDistributionJunction, oid: -1)]
So, I deleted the entire data from the geodatabase -> Ran the "Stage Utility Network" and then "apply Asset package from the scratch.