Schema

interface InterfaceA { id: ID! }
interface InterfaceB { name: String! }
type Person implements InterfaceA, InterfaceB { id: ID!, name: String! }
type QueryRoot { value: InterfaceA }
schema { query: QueryRoot }

Query

{ value { ... on InterfaceB { name } } }

This should work since Personimplements InterfaceA and thus, InterfaceB should be part of the valid fragment types for value. But currently, the validator throws an error due to incorrect buildup of :valid-fragment-spreads in the analyzer.