Typecasting causing struct values to change (Swift)

After downcasting an array of structs, my Variables View window shows that all of the values in my struct have shifted "down" (will explain in a second). But when I print(structName), the values are fine. However, when I run an equality check on the struct, it once again behaves as though my values have shifted.

For example, I am trying to downcast Model A to ModelProtocol. var m = Model A and has the values {id: "1234", name: "Cal"}. When I downcast, m now has the values { id:"\0\0", name:"1234" }.

Actual Example Below:

Models that I want to downcast:

struct PrivateSchoolModel: Decodable, SchoolProtocol {
    var id: String
    var name: String
    var city: String
    var state: String
}
struct PublicSchoolModel: Decodable, SchoolProtocol {
    var id: String
    var name: String
    var city: String
    var state: String  
    var latitude: String
    var longitude: String
}

Protocol I want to downcast to:

protocol SchoolProtocol {
    var id: String { get set }
    var name: String { get set }
    var city: String { get set }
    var state: String { get set }
    var longitude: Float { get set }
    var latitude: Float { get set }
}

extension SchoolProtocol {
    var longitude: Float {
        get { return -1.0 }
        set {}
    }
    var latitude: Float {
        get { return -1.0 }
        set {}
    }
}

Downcasting:

guard let downcastedArr = privateSchoolArray as? [SchoolProtocol] else { return [] }

Result (item at index 0) or originalArr:

id = "1234"
name = "Leo High School"
city = "Bellview"
state = "WA"

Result (item at index 0) of downcastedArr:

id = "\0\0"
name = "1234"
city = "Leo High School"
state = "Bellview"

But if I print(downcastArr[0]), it will show:

id = "1234"
name = "Leo High School"
city = "Bellview"
state = "WA"

But if I try originalArray[0].id == downcastArr[0].id, it returns false

My Code with the problem:

class SchoolJSONHandler {
    private enum JSONFile: String {
        case publicSchool = "publicSchool"
        case privateSchool = "privateSchool"
    }

    private lazy var privateSchoolArray = getPrivateSchools()
    private lazy var publicSchoolArray = getPublicSchools()

    func getSchoolArray(sorted: Bool, filtered: Bool, by stateAbbreviation: String?) -> [SchoolProtocol] {
        var schools = combineArrays()

        if sorted {
            schools.sort(by: { $0.name < $1.name })
        }

        if filtered {
            guard let abbr = stateAbbreviation else { return [] }
            schools = schools.filter {
                return $0.state == abbr
            }
        }

        return schools
    }

    private func combineArrays() -> [SchoolProtocol] {
        // EVERYTHING IS FINE IN NEXT LINE
        let a = privateSchoolArray
        // PROBLEM OCCURS IN NEXT 2 LINES WHEN DOWNCASTING
        let b = privateSchoolArray as [SchoolProtocol]
        let c = publicSchoolArray as [SchoolProtocol]
        return b + c
    }

    private func getPublicSchools() -> [PublicSchoolModel] {
        guard let jsonData = getJSONData(from: .publicSchool) else { return [] }
        guard let schools = decode(jsonData: jsonData, using: [PublicSchoolModel].self) else { return [] }
        return schools
    }

    private func getPrivateSchools() -> [PrivateSchoolModel] {
        guard let jsonData = getJSONData(from: .privateSchool) else { return [] }
        guard let schools = decode(jsonData: jsonData, using: [PrivateSchoolModel].self) else { return [] }
        return schools
    }

    private func getJSONData(from resource: JSONFile) -> Data? {
        let url = Bundle.main.url(forResource: resource.rawValue, withExtension: "json")!
        do {
            let jsonData = try Data(contentsOf: url)

            return jsonData
        }
        catch {
            print(error)
        }

        return nil
    }

    private func decode<M: Decodable>(jsonData: Data, using modelType: M.Type) -> M? {
        do {
            //here dataResponse received from a network request
            let decoder = JSONDecoder()
            let model = try decoder.decode(modelType, from:
                jsonData) //Decode JSON Response Data

            return model
        } catch let parsingError {
            print("Error", parsingError)
        }

        return nil
    }
}

And then it is just called in another class by schoolJSONHandler.getSchoolArray(sorted: true, filtered: true, by: "WA")