AttributeError: 'dict' object has no attribute '_sa_instance_state' with SQLAlchemyAutoSchema

running into a weird issue with sqlalchemy where I'm getting AttributeError: 'dict' object has no attribute '_sa_instance_state' and is coming from here:

    schema = ApplicationSchema()
    new_application = schema.load(body, session=db.session)

The model looks like this:

class ApplicationSchema(SQLAlchemyAutoSchema):  # noqa
    class Meta:
        model = Application
        include_relationships = True
        load_instance = True
    applicant = fields.Nested("ApplicationApplicantSchema", default=None)    
    legalDocs = fields.Nested("ApplicationLegalDocsSchema", default=[], many=True) 

class ApplicationApplicantSchema(SQLAlchemyAutoSchema):
    applicantId = fields.Int()
    firstName = fields.Str()
    middleName = fields.Str()
    lastName = fields.Str()
    birthDate = fields.Str()
    ssn = fields.Str()
    phoneNumber = fields.Str()
    emailAddress = fields.Str()
    addressLine1 = fields.Str()
    addressLine2 = fields.Str()
    city = fields.Str()
    state = fields.Str()
    zip = fields.Str()
    timestamp = fields.Str()

class ApplicationLegalDocsSchema(SQLAlchemyAutoSchema):
    documentId = fields.Int()
    applicationId = fields.Int()
    link = fields.Str()
    type = fields.Str()
    timestamp = fields.Str()     

 

I have a similar model for applicants that looks the same but works:

        # Create a applicant instance using the schema and the passed in applicant 
        schema = ApplicantSchema()
        new_applicant = schema.load(applicant, session=db.session)

        # Add the applicant to the database
        db.session.add(new_applicant)
        db.session.commit()

models for that look like this:

class ApplicantSchema(SQLAlchemyAutoSchema):  # noqa
    class Meta:
        model = Applicant
        load_instance = True
        include_relationships = True
    applications = fields.Nested("ApplicantApplicationSchema", default=[], many=True)    

unsure why one works but the other doesn't?