Underscore is added to links in view
After much work I came up with a workaround. My first thought was to add a Twig filter to views-view-row-rss.html.twig like so &lt;link&gt;{{ link | replace('_', '') }}&lt;/link&gt; but the underscore was still being displayed, which told me that either 1. the Twig filter wasn't working or 2. the underscore was being applied later in the render process.

The Twig template's documenation made reference to a template_preprocess_views_view_row_rss() hook I found implemented in /core/modules/views/views.theme.inc so I added the following hook to my custom.theme PHP file:

function ncei_preprocess_views_view_row_rss(&amp;$variables) {
  $item = $variables['row'];
   $variables['title'] = $item-&gt;title;

   //$variables['link'] = $item-&gt;link;
   $variables['link'] = str_replace("_", "", $item-&gt;link);

   if (isset($item-&gt;description) &amp;&amp; is_array($item-&gt;description)) {
     $variables['description'] = (string) \Drupal::service('renderer')-            
       &gt;render($item-&gt;description);
   }

 $variables['item_elements'] = [];
 foreach ($item-&gt;elements as $element) {
   if (isset($element['attributes']) &amp;&amp; is_array($element['attributes'])) {
     $element['attributes'] = new Attribute($element['attributes']);
   }
   $variables['item_elements'][] = $element;
 }
}    


I commented out the original line above for reference, but I'm setting the link variable to the item's link, stripped of all undertscores. This isn't the best solution, and will break if the link actually contains underscores, but it worked as a temporary workaround in the meantime.