Combined CSS is loaded but not executed

<%- if @topic_view.topic.tags.present? %>
<%= t 'js.tagging.tags' %>: <%- @topic_view.topic.tags.each do |t| %> <%= t %> <%- end %>
<% end %>

Silverstripe Version: 4.4

Question:

in the page.php i have put the code for the merge. the merged CSS file is also created in “public/assets/_combinedfiles” on the server (comb-style-62cde17.css).
Also the path to the CSS file is output properly in the . However, the CSS file is not loaded. In the dev tools under “network” a 200 code is displayed. If I select an HTML element in the code via “Elements”, then the CSS file and the corresponding classes are not displayed in “Styles”.
In pupic/.htaccess the rewrite base is up: RewriteBase ‘/public’.
Question: Why is the loaded CSS not executed?

        protected function init()
        {
            parent::init();

			Requirements::combine_files('public/assets/_combinedfiles/comb-style.css', 
			[
				'_resources/themes/xyz/css/bootstrap.css',
				'_resources/themes/xyz/css/revolution-slider.css',
				'_resources/themes/xyz/css/slick.css',
				'_resources/themes/xyz/css/style.css',
				'_resources/themes/xyz/css/responsive.css'
				]
			);