I found this very interesting. I already blocked those pages via robots.txt but it keeps on showing on my Search Console for Smartphone. Does adding this:

User-agent: Googlebot-mobile 
Allow: /*?variant=*

will make the error disappear?

The general robots.txt is:

User-agent: *
Disallow: /*?variant=*
  • Search console data is not real time, they might showing your 1 month old data, it will be great if you test those URL on live Google search. – Goyllo Jun 22 '18 at 4:15
  • What section of Google Search Console are they appearing in? – Stephen Ostermiller Jun 22 '18 at 10:15