Super long wifi request travel time on iPhone 8 / iPhone X - ios

Question

Not sure if it's ok to ask this here but I'm now confronting this frustrating problem and would like to ask for opinion on how to deal with this.
From some of the forum and discussions, looks like iPhone 8 and iPhone X has super slow internet issue when using wifi and running on iOS 11.4 / 11.4.1, and this results to the request travel time rediculously increases to almost 55 seconds (e.g. Hello world pinging test API) for a very simple request in my app. If I turn the wifi off and use 4G instead, the same request travel time is only 2 seconds(the API server is in the US while the app is oversea, so generally bearable), and the same request only travels 2 - 3 seconds on iPhone 6 plus running on iOS 11.2 / 11.4.1 in wifi mode.
I guess this is more a hardware or system side bug and on the app side we may not be able to do anything about this. However, as our client users who use iPhone 8 are unhappy about the waiting time and insist on solving it, and I also found that if I call the hello world API from safari browser of the iPhone, things are not that bad. Therefore, I would like to know if there is anything the app side can do (ex. detect this issue and do the workaround) to fix this or sooth the awful user experiences?
P.S. My app is written in Swift and I don't use third party library such as Alamofire to manage requests, simply use the build-in functionalities in Foundation. I would like to post some code on my sending request here, even if this may not help much.
func sendRequest(request: URLRequest, completion: #escaping (Int, Data?, Error?) -> Void) {
let task = URLSession.shared.dataTask(with: request) {data, response, error in
guard let data = data, error == nil else {
print("HTTP request error=\(String(describing: error))")
// use 999 to represend unknown error
completion(HTTPHelper.DEFAULT_STATUS_CODE, nil, error)
return
}
guard let httpStatus = response as? HTTPURLResponse else { // check for http errors
return
}
if(httpStatus.statusCode != 200) {
print("statusCode should be 200, but is \(httpStatus.statusCode)")
print("response = \(String(describing: response))")
}
do {
let json = try JSONSerialization.jsonObject(with: data, options: .allowFragments)
print(json)
} catch {
print("error serializing JSON: \(error)")
}
let responseString = String(data: data, encoding: .utf8) ?? ""
print(responseString)
completion(httpStatus.statusCode, data, nil)
}
task.resume()
}
And this is the function where the above request is called, the request travel time is the time elapsed between two [TIME FLAG]:
func test(completion: #escaping (Bool) -> Void) {
let url = httpHelper.myUrlBuilder()
let request = httpHelper.wrapGetRequest(url: url, withToken: .none)
NSLog("[TIME FLAG] Test request sent")
httpHelper.sendRequest(request: request as URLRequest) { statusCode, data, error in
NSLog("[TIME FLAG] Test response get")
guard error == nil && self.httpHelper.validateStatusCode(statusCode: statusCode) else {
completion(false)
return
}
completion(true)
}
}
Thanks for any kind of answers and feedbacks.