Twig adds an unwanted 'row' class that doesn't appear in class array
Those 5 classes are being added using .addClass() to a pre-existing {{ attributes }} Twig object. The 'row' class must already be in the attributes object when Drupal passes it to the Twig template.
Typically, the place where something like that would happen is in your .theme file (or the parent theme's .theme file if yours is a subtheme). Look for a function like THEMENAME_preprocess_region() and see if you can find a hard-coded &quot;row&quot; string being thrown in there.
Alternatively, some fancier theme systems might expose configuration options in the Drupal interface that could be setting that class. You'd find those under Admin &gt; Appearance, then in &quot;Settings&quot; for your active theme.