Check the background processes. Go to Tools & Administration > Portal Settings > Background Processes. Check the status respectively the activity of export2feed, as well as the timeframe of the export.
Check if there is a link to the RSS Feed in the sourcecode in the HTMH-Head. Got to Tools & Administration > Design & Layout > Design Moduls. In the area Other Layout Elements you find the module htmlHead where you can check if the placeholder „$feedLinks“ is in the sourcecode, e.g.: