Mail not showing Yahoo "Sent" messages

Yesterday my Mac Mail stopped showing all "sent" email messages under my Yahoo account since December 2019. Even messages I have sent since this started do not appear in the Yahoo account "Sent" folder. I can see all sent messages if I go to All Sent (even there, they show up under All Sent, but not under the Yahoo subfolder of All Sent).

I still see all current messages in the Yahoo account Inbox. It is only the Sent messages that have disappeared from the Yahoo account.

How can I get them back?