A family member has a problem with Yahoo Mail that is new to me. All her emails older than a couple of weeks ago no longer appear in her inbox-- sorting newest to oldest does not scroll past a certain point a couple of weeks ago. Sorting oldest to newest starts at the same point a couple of weeks ago. Some few emails, nothing newer than six months ago, appear in Archive.
Here is some evidence that this is not a case where the user accidentally deleted everything: searching for a correspondent by email address returns the statement that "You and appeared together on 226 messages between Feb 2016 and Aug 2018." But only four messages (three from the last couple of weeks and one from 2014) are visible. See screen shot.
The Yahoo "support" and "help forum" have not responded. Any ideas?