If your server was setup properly, it should not allow listing of files when URL accesses a folder on your website. If you cannot set it in your hosting options (you should be able to do that), you will need to include the below in your .htaccess file:
# Block directory listing.
# This should already be default on your server, and is disabled here because it creates errors on some servers.
The above is code from the X3 .htaccess, but commented out, because we don't by default include rules that are not related to X3.
So basically, if Google finds this page, it may (or may not) index it. It should be FORBIDDEN. Why search console reports it a mobile issue or whatnot is irrelevant.
andreamarucci wrote:Quite strange that this page is in the sitemap I think but the question is how to fix this problem.
Google finds whatever it wants to find, and does not care much about sitemaps. If a page/file is available, chance is Google will find it.