found the culprit

themes/lumbung-theme/layouts/partials/pen_card.html

@@ -29,11 +29,13 @@
           {{$matches := findRESubmatch `<img\s.*?src=(?:'|")([^'">]+)(?:'|")` .Content 1 }}
           {{range $matches}}{{$first_image = index . 1}}{{end}}
             {{with .Resources.Get $first_image}}
+              {{if .ResourceType}}
               {{.ResourceType}}
               {{.MediaType}}
               <img src="{{ .Permalink }}" alt="">
               {{/* uncomment below to crash the build*/}}
-              {{/* .Width */}}
+              {{.Width}}
+              {{end}}
               {{end}}
           <footer class='post-footer'>
             <a href="{{ .RelPermalink }}">