If you are using WKWebview which is the default webview in IOS 11 as per the official blog post, you need to rewrite the file://
url before using in your HTML.
If you’re working with local files (text files, images, videos), you’ll need to make sure that the path of file does not have file:// in front of it.
import { normalizeURL } from 'ionic-angular';
And in your function,
this.imagePath = normalizeURL(path);
return path;
Further check troubleshooting section which says the same.