StrawberryShake: Mutation containing a union with nested data fails to generate code

[ChrisMH]

UserSetting.zip

preview.27

I have a mutation that returns a union where one part has a nested data structure:

mutation StoreUserSettingFor($userId: Int!, $customerId: Int!, $input: StoreUserSettingForInput!) {
    storeUserSettingFor(userId: $userId, customerId: $customerId, input: $input) {
        ... on UserSettingSuccess {id}
        ... on UserSettingError {errors {code message}}
    }
}

When building the above, code generation returns: CSC : error SS0006: The given key 'StrawberryShake.RuntimeType' was not present in the dictionary. [C:\Users\chogan\DevO\ovc-source\WebService\GraphTest\GraphTest.csproj]

I have tried removing the other arm of the union with the same error message:

mutation StoreUserSettingFor($userId: Int!, $customerId: Int!, $input: StoreUserSettingForInput!) {
    storeUserSettingFor(userId: $userId, customerId: $customerId, input: $input) {
        ... on UserSettingError {errors {code message}}
    }
}

I don't know for sure that it's the nested data, but UserSettingSuccess, which is flat, works, and the other doesn't.

[PascalSenn]

@ChrisMH can you share your schema too? I could not reproduce this issue

[ChrisMH]

@PascalSenn Attached