第二页加载后css错误

I am having a problem on a wordpress website, when loading the site for the first time all over load properly, if I try to reload the page you can see a problem (seems to be a css problem), this only happens if you use the button reload of the browser, if I click on the logo link or send with keyboard this does not happen

This problem occurs only when it is activated the plugin https://it.wordpress.org/plugins/bwp-minify/

when i see the problem , in chrome console i see some error example :

<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/ppp/public_html/wp-content/plugins/bwp-minify/min/lib/HTTP/ConditionalGet.php:360)

this is the website where i found the problem http://shoutkey.com/jicama

similar problem is also mentionated on this discussion CSS fails to load after refreshing a page. After the second refresh it works again and so on