WKWebView Delegate WKNavigationDelegate fails to set properly in production

We have detected in production that there are times when we try to set the WKNavigationDelegate of the WKWebView, but that even though the object we are assigning to the delegate is not nil, the result of the command to set the delegate is that the web-view's delegate remains nil.

Essentially as a step by step what happens is:

1. Create and retain a WKWebView: "self.webView = WKWebView()"
2. set self as the navigation delegate: "self.webView.navigationDelegate = self"
3. record to remote logging if this assignment has been successful: "operationalLogger.webViewDelegates(webview.navigationDelegate != nil)"

We are observing in our logging that in ~7% of cases the webview.navigationDelegate is equal to nil, even after assigning a fully allocated WKNavigationDelegate object to the instance.

Class where we set the delegate:

import WebKit

class WebViewContainer: NSObject {
    
    private static var sharedInstance: WebViewContainer?
    
    let webView: WKWebView
    var webViewContainerNavigationDelegate: WKNavigationDelegate?
    var webViewContainerUIDelegate: WKUIDelegate?
    
    // Use this standard init function to create a new instance
    init(config: WKWebViewConfiguration?) {
        
        if let configExists = config {
            self.webView = WKWebView(frame: .zero, configuration: configExists)
        } else {
            self.webView = WKWebView()
        }
        
        super.init()
        self.webView.navigationDelegate = self
        self.webView.uiDelegate = self
    }
    
    // Use this shared function to use a Singleton instance
    static func shared(config: WKWebViewConfiguration?) -> WebViewContainer {
        
        guard let existingInstance = sharedInstance else {
            let newShared = WebViewContainer(config: config)
            sharedInstance = newShared
            return newShared
        }
        
        return existingInstance
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

extension WebViewContainer: WKNavigationDelegate {
// Implemented WKNavigationDelegate here
}

Please note that this Container class has been created so that we can test if the success rate improves when we use a Singleton WKWebView, however this does not improve the result.

Unfortunately I'm unable to reproduce this locally, but I can see from our logs that in ~7% of cases our users are affected by this issue. I will send more information if I am able to. Please let me know if there's anything we can do to stop this happening, as it's affecting the functionality of our app in production. Thanks