We are using SharePoint 2013 on-premises enterprise version. The search function on our site not returning results and ending up with no resource found. Before a week it was working fine but now it's not. Below are the errors I found in central admin under search service administration.
Check if TLS 1.1 and TLS 1.2 are installed on the server. If they are, try to re enable them to open a connection. This issue is usually caused because there is no SSL Protocol available on the server to communicate with sharepoint search servers.