When projects make journal posts within a month of each other (it seems) of their last, the older post shows up as the headline on the home page for some reason. Note in this screenshot how the journal post " July 2020 Photo-observation of the Month" is highlighted, but the posting date is August 27th. It does say that there are two “new” posts, but the newest one is actually, “Don’t Forget to Fav Photos for the August Winner!” which took some digging to find. Clearly, the newest post, even if there are multiple “new” posts, should be shown in the banner.
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What you say makes sense to me; I expect staff and/or moderators will have more cogent comments. :)