old css files in minify folder

Hi
Once I had some problems with the plugin and I delete w3 total cache and installed wp super cache. Less than a day I delete that and reinstall W3. Now I have problem with my theme css files in some cases and the theme author says there is some old css files in cache folder that to rule the css and don’t let the theme css files to act correctly (for example titles font not changing any more).
I emptied the minify cache but nothing in that folder changed. If I delete the css files in the minify folder by FTP it will cause any problem? Can I do that?

https://ww.wp.xz.cn/plugins/w3-total-cache/