Try different check

webapp_conversation.py

@@ -99,7 +99,7 @@ def html_conversation_view(post_id: str,
                                     minimize_all_images, None)
         if post_str:
             # check for "HTTP/1.1 303 See Other Server"
-            if not post_str.startswith('HTTP/'):
+            if 'X-AP-Instance-ID' not in post_str:
                 conv_str += text_mode_separator + separator_str + post_str
 
     conv_str += text_mode_separator + html_footer()