My CSS suddenly doesn’t load anymore

I’ve did some small changes on my CSS, nothing crazy, uploaded them to my website. Cleared my cache and suddenly, the website doesn’t show my custom styles.

Website: http://experienceantwerp.be/

My styles are included in the enqueue.php file, but it always worked.

if (!function_exists('understrap_scripts')) {     /**      * Load theme's JavaScript and CSS sources.      */     function understrap_scripts()     {         // Get the theme data.         $  the_theme = wp_get_theme();         $  theme_version = $  the_theme->get('Version');          wp_enqueue_style('slider-slider-styles', 'https://cdnjs.cloudflare.com/ajax/libs/slick-carousel/1.8.1/slick-theme.min.css');         wp_enqueue_style('lity-style', 'https://cdnjs.cloudflare.com/ajax/libs/lity/2.4.1/lity.min.css');         $  css_version = $  theme_version . '.' . filemtime(get_template_directory() . '/css/theme.min.css');         wp_enqueue_style('understrap-styles', get_stylesheet_directory_uri() . '/css/theme.min.css', array(), $  css_version);          }     } } // endif function_exists( 'understrap_scripts' ).  add_action('wp_enqueue_scripts', 'understrap_scripts', 10); 

If I check my source code in the browser, it seems that the slider-slider-styles and lity-style are loaded, but not my styles "understrap-styles".

The file is available on the server because I can directly open the file in my browser.