Move inside concerns or the override won't work

app/models/tag/attachable.rb

@@ -3,9 +3,9 @@ module Tag::Attachable
 
   included do
     include ActionText::Attachable
-  end
 
-  def attachable_plain_text_representation(...)
-    "##{title}"
+    def attachable_plain_text_representation(...)
+      "##{title}"
+    end
   end
 end

app/models/user/attachable.rb

@@ -3,9 +3,9 @@ module User::Attachable
 
   included do
     include ActionText::Attachable
-  end
 
-  def attachable_plain_text_representation(...)
-    "@#{first_name.downcase}"
+    def attachable_plain_text_representation(...)
+      "@#{first_name.downcase}"
+    end
   end
 end