Falcon13 is right. I had the same issue on https://kingstonmass.com/ma-ski-reports/. Here’s the fix: Copy all the code in snow-report.php to an editor and search for the string snow.rss .
Change both instances of snow.rss to snow-rss.html , recopy and paste it back to the edit plugin window, save changes and it will work as advertised. You can also use the replace function, using “find what” snow.rss and “replace with” snow-rss.html to do the same. Thanks to Falcon for helping with the correct answer!