Here is code, stuck with that simple issue which I never have had in past 7 years:

```
<html>
<body>
    <iframe></iframe>
    <script>
        window.frames[0].document.write('<scr' + 'ipt type="text/javascript" src="//code.jquery.com/jquery-3.0.0.min.js"><\/scr' + 'ipt>');
    </script>
</body>
</html>

```

The problem is that browser's spin wheel continue to circle.

Network console shows all loaded.

If I remove iframe from DOM, or add/change @src attribute - loading stops.