Due to a database error that occurred during on of the deferred tasks when you deleted your test pages that were already in the feed, the connections of those test pages to the feed were not removed. So there are several feed entries which point nowhere that are actually newer than the remaining feed entries.
You can cleanup the orphan entries manually by running a MySQL query:
Code:
DELETE feeditem
FROM vw_feeditem AS feeditem
LEFT JOIN vw_page AS page ON (page.pageid = feeditem.pageid)
WHERE page.pageid IS NULL
Afterwards, run:
Code:
TRUNCATE TABLE vw_feedcache
The related database error is fixed in the next build, and these queries will be run by the next upgrade. The error appeared in 4.0.21.