#2 May 04, 2018 22:02
May be this is a matter of Chache-Management.
In Features > Posts > RSS/Atom feeds I set "Posts in feeds" to 30 and
deactivated in widget "XML Feeds (RSS / Atom)" in container "Sidebar" "Allow caching:" (in other collections in which caching was not enabled the problem does not exist. Therefor I presume, the bug may root in cache management.)
Now; also the latest post is listed in RSS Feed.
Hope, that the next post will be added to the list. I will keep you updated ;-)