I have some website running with PHP. In my .htaccess I have added the following directives:

<FilesMatch "index.php">
        Header add Link "</css/bootstrap.min.css>; rel=preload; as=style"
</FilesMatch>

The websites main content is solely called via the index.php, like this https://somedomain.com or https://somedomain.com/?feature=a.

Within the website I am using Ajax to call further data, from URIs like https://somedomain.com/ajax.php?load=this.

Recently Google Chrome started throwing warnings in the dev console with every Ajax call that is done, like that:

The resource was preloaded using link preload but not used within a few seconds from the window's load event. Please make sure it has an appropriate as value and it is preloaded intentionally.

Is that a bug in Chrome or is there something wrong with my .htaccess?

Thank you.