line 8 is correct
from your website's generated feed
line 8 is missing the required language information.
open the language editor.
"en-us" is missing from your RSS_LANG string
typed exactly as shown in the screenshot. no quotes.
Update Language File
then go to the
(Tools & Information group in the control panel) and
to rebuild the feed.
this should correct your bad feed.
there are two different types of "RSS Feeds."
UBB.threads generates RSS 2.0 feeds.
Your feed reader should be using RSS 2.0 format, not ATOM.https://problogger.com/rss-vs-atom-whats-the-big-deal/
There is a fun story behind the two. I believe it is here:https://en.wikipedia.org/wiki/Atom_(Web_standard)#Atom_compared_to_RSS_2.0
Additional reading here:https://en.wikipedia.org/wiki/RSS