On my end, it was due to call [self.webView loadFileURL:fileURL allowingReadAccessToURL:accessURL]; multiple times, even though it was worked on earlier version. here is the response from Apple side The loadFileURL:allowingReadAccessToURL: call should be made only once, after all the resource files have been copied. The CSS and image files don't need to be loaded individually — they will be loaded automatically by the HTML when it references them, because your accessURL grants WKWebView read access to the entire cv_webroot directory. Here is what the corrected flow should look like: hope this helps.

Thanks Apple, I filed DTS ticket, and get the solution from Apple Engineer. It is resolved.

here is error signature: start setting access permission file:///var/mobile/Containers/Data/Application/9044BAAF-5152-4C71-A3BA-5292C6FEED70/Documents/cv_webroot/CM_chat_view_base.html with accessURL file:///var/mobile/Containers/Data/Application/9044BAAF-5152-4C71-A3BA-5292C6FEED70/Documents/cv_webroot/ 0x12c0d40c0 - [PID=1514] WebProcessProxy::hasAssumedReadAccessToURL(3198190): no access complete setting access permission file:///var/mobile/Containers/Data/Application/9044BAAF-5152-4C71-A3BA-5292C6FEED70/Documents/cv_webroot/CM_chat_view_base.html with accessURL file:///var/mobile/Containers/Data/Application/9044BAAF-5152-4C71-A3BA-5292C6FEED70/Documents/cv_webroot/