Hello,
You should not use png instead of jpg. It’s different formats of image and you can google about difference between them and when you should use one and when another. We meant that problem appears with jpg images only. Could you, please, try default VC element image and check if this issue appears with default element or with our element only. If problem persists even with default Image element then enable default WP theme – Twenty Seventeen for example and check again: problem persists even with default theme or with our theme only.
In case issue appears with our theme only and with our element only then provide admin panel and FTP access to your site.
Regards