Issue:
Clicking “SHOW MORE POSTS” on your site’s feed does not display posts older than 7 days.
Cause:
The Newsfeed is configured to display posts that are available in the Feed Cache. By default, the feed cache only retains posts from the last 7 days. Any post older than that will not be displayed when you click “SHOW MORE POSTS”.
Solution:
Increase how long posts are stored in the cache with the following PowerShell script. In my example, I increase it to 30 days (720 hours).
Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue
$upa = Get-SPServiceApplication | where {$_.TypeName -Like "User Profile Service Application"}
$upa.FeedCacheTTLHours = 720
$upa.Update()
SharePoint Mustard 