Hello Tim,
Thank you for your question and I am happy to answer.
It’s not the W3 Total Cache that treat mobile differently than Desktop, it’s the Google Page Speed insights.
As I’ve mentioned in the previous post, only Minified CSS files can be eliminated as render-blocking and as I can see, either Minify is not enabled at all in Performance>General settings or CSS Minify is not enabled in Performance>Minify
You should enable CSS Minify, make sure that the option “Eliminate render-blocking CSS by moving it to HTTP body” is enabled, save all settings and purge the cache.
I hope this helps!
Thanks!