Tilda ~ keeps reappearing in Mail

In Apple Mail on my iMac, I keep the tilda on one or more of my email accounts instead of showing me how many if any unread emails are in that inbox.

Double clicking on the individual mail account has not worked to fix it but going to one of the mailboxes below and then double clicking on the mail within will fix the problem for a few hours or a day. Then the problem recurs.

I have tried the Connection Doctor over and over and it makes no difference. Some of the accounts will respond properly if I double click on mail residing in a mailbox or in the Trash mailbox.

A few days ago I posted a similar message and thought at the time that Connection Doctor was fixing the problem but the problem keeps recurring and one of the accounts simply will not clear the tilda.