Old Email Showing Up as Unread

I am using K9 version 6.602 on my Galaxy S22 phone. I am constantly getting old email showing up in my inbox as unread. This happens multiple times a day. Sometimes they disappear and show up again later. I can have as many as 10-12 emails that show up as unread, some are from earlier year and sometimes earlier. My wife uses the same app on her phone and is not experiencing this problem.