[Theme: Basic] Mobile view not updating CSS

Hi, I’m using my own modified version of Themify’s ‘Basic’ theme. After updating it to the latest version, it seems like any changes I make to any CSS is not loaded at all on mobile phones. Not just mobile-targeted CSS; any CSS at all. The CSS itself loads, everything is styled correctly, but if I make any changes, like changing the colour of text, it shows up fine on the desktop version but on the mobile version it will show the old text colour. This only seems to be affecting CSS and nothing else. I have no plugins at all, WordPress is up-to-date.

Website URL is http://www.andrewfender.co.uk.

Thanks for any help.