Update RNCWKWebView.m

ios/RNCWKWebView.m

@@ -95,6 +95,8 @@ static NSString *const MessageHanderName = @"ReactNative";
     [self addSubview:_webView];
 
     [self visitSource];
+  } else {
+    [_webView.configuration.userContentController removeScriptMessageHandlerForName:MessageHanderName];
   }
 }