Can't Enable Minification

I too face this problem, but no solution yet other than using a separate WordPress plugin for minification.

Same issue on my site.

Did you enable CDN cloudflare extension in w3tc?

This article from Cloudflare mentions something about not to use both minify in w3tc and cloudflare

https://support.cloudflare.com/hc/en-us/articles/200169756-Can-I-use-WordPress-caching-plugins-like-Super-Cache-or-W3-Total-Cache-W3TC-with-CloudFlare-

I don’t understand the detail, but after I turned off the cloudflare extension, I can tick the enable minify box again.