Here is the text from WPBakery support
The issue is because the older visual composer (now WPBakery Page Builder) was modified by the theme author by customizing the existing elements and adding the new one’s.
Now when you updated it, the customization made by the theme author was lost which causes the issue.
You can check it with the theme author if there is any way to preserve the customization done by him/her with the latest version, so that such an issue can be avoided at your end.
Thanks in advance