Emails disappearing on iPhone/iPad

My wife’s emails keep disappearing on her iPhone and iPad.  We have not changed her settings for years and about a week ago, the emails started to disappear and her inbox is empty.  When I send her a test email, it shows up in her inbox, but then after a minute or two is just disappears.  I then send her another email, it shows up, but then disappears after a few minutes. 

This behavior is the same on her iPad.  My Cox emails work fine on my phone and her phone.  I then setup a second email account for my wife and added the account to her phone and the emails are fine with this account.  I also installed the myMail app on her phone and the same thing happens, so it must have something to do with the Cox email system and account.  Her phone email settings are the IMAP settings “imap.cox.net” and they are exactly the same as mine.