func loadURL(_ request: URLRequest) {         navigationDelegate = self         uiDelegate = self         load(request)         scrollView.delegate = self     }          func loadURL(_ path: String) {         navigationDelegate = self         uiDelegate = self                  let url = URL(fileURLWithPath: path)         let data = try! Data(contentsOf: url)         let baseURL = url.deletingLastPathComponent()                  load(data, mimeType: "application/pdf", characterEncodingName: "", baseURL: baseURL)                  scrollView.delegate = self     } } extension ProdWebView: WKNavigationDelegate {          func webView(_ webView: WKWebView,                  didStartProvisionalNavigation navigation: WKNavigation!)     {         webViewDelegate?.start()     }          func webView(_ webView: WKWebView,                  didFailProvisionalNavigation navigation: WKNavigation!,                  withError error: Error)     {         trace?.stop()         webViewDelegate?.error(error)     }          func webView(_ webView: WKWebView,                  didFinish navigation: WKNavigation!)     {         trace?.stop()         webViewDelegate?.stop()     } When user click on The Links double times .... I am getting crash I can see in auto logs code = -999 error 2021-10-03 21:04:43.113096+0530 eTradeMX[22419:6003510] [Process] 0x1070a1818 - [pageProxyID=5, webPageID=6, PID=22420] WebPageProxy::didFailProvisionalLoadForFrame: frameID = 3, domain = NSURLErrorDomain, code = -999 But below delegate method is not calling . Some times its calling some Times not calling . I was written delegates also   weak open var navigationDelegate: WKNavigationDelegate?     weak open var uiDelegate: WKUIDelegate?     navigationDelegate = self     uiDelegate = self   func webView(_ webView: WKWebView,          didStartProvisionalNavigation navigation: WKNavigation!) expect this didStartProvisionalNavigation remaining delegates are calling properly .