Wow. Has that changed recently? I've been using both x and x pro for some time now and previously, I was able to add the filter just like I've done so for blog posts here: https://www.littlelovelies.com.au/blog/
Also, the portfolio filter added via visual composer works perfectly well on another one of my sites: https://www.kcreative.com.au/ You can see it has been added on the homepage which is not the native portfolio page.
It worked previously with X Pro - I've just noticed it is not working with the latest version of X Pro 2.2.5
Thanks again in advance for looking into this issue.