Category Featured Images Extended (CFIX) does not work with Visual Composer and other page or site builders – or themes – that use their own logic to extract or display featured images. You might be able to meld the two together, but it would be a developer task. However, I do have a plug-in, long in Beta, that may provide an answer, if you use the option to save category image as featured image. While CFIX provides the featured image on the fly, the successor provides this alternative option, which is also somewhat more performant: https://ckmacleod.com/sdm_downloads/thumbnail-featured-image-fallbacks/
The plugin has some additional features, and is designed to take up CFIX image assignments when you install it. I’ve been using it without problems for a couple years actually. I’ve just been too busy to finalize and upload it to WordPress. However, if you try it, please observe all precautions that normally apply to use of beta versions of plugins, including creation of a good backup. Also, please let me know how it goes!
