In WKWebView having issue to write and read its taking some time , So when you fetch the cookie some time you will get updated cookie but sometime it will be old one, and you will get error on any server request. I was facing this issue in 3 Days , 
Solution: No need to store cookies in WKWebsiteDataStore.
Getting cookies:
Swift:
extension WKWebView {
private var httpCookieStore: WKHTTPCookieStore  { return WKWebsiteDataStore.default().httpCookieStore }
func getCookies(for domain: String? = nil, completion: @escaping ([String : Any])->())  {
        var cookieDict = [String : AnyObject]()
        httpCookieStore.getAllCookies { cookies in
            for cookie in cookies {
                if let domain = domain {
                    if cookie.domain.contains(domain) {
                        cookieDict[cookie.name] = cookie.properties as AnyObject?
                    }
                } else {
                    cookieDict[cookie.name] = cookie.properties as AnyObject?
                }
            }
            completion(cookieDict)
        }
    }
}
Objective-c :
-(void )getAllCookies
{
    NSMutableString *updatedCockies= [[NSMutableString alloc] init];
    if (@available(iOS 11.0, *)) {
        WKHTTPCookieStore *cookieStore = _webView.configuration.websiteDataStore.httpCookieStore;
        NSLog(@"cookieStore *********************: %@",cookieStore);
        [cookieStore getAllCookies:^(NSArray* cookies) {
            NSHTTPCookie *cookie;
            for(cookie in cookies){
               NSLog(@"%@",cookie)
            }
            self->updatedCookie = updatedCockies;
            NSLog(@"cookie *********************: %@", self->updatedCookie);
        }];
    }
}
Every time you want new cookie so you need to write below code:
 Given Sharpio 
Swift : 
let config = WKWebViewConfiguration()
if #available(iOS 9.0, *) {
    config.websiteDataStore = WKWebsiteDataStore.nonPersistentDataStore()
} else {
     // I have no idea what to do for iOS 8 yet but this works in 9.
}
let webView = WKWebView(frame: .zero, configuration: config)
Objective C-- 
WKWebViewConfiguration *wkWebConfig = [WKWebViewConfiguration new];
    wkWebConfig.websiteDataStore = [WKWebsiteDataStore nonPersistentDataStore];
self.webView = [[WKWebView alloc] initWithFrame: CGRectZero
                                      configuration: wkWebConfig];
*******Every time you will get new cookies********