Problem with checking one of four POP3 accounts

Hello maybe you can help me. Have had and have been using K9 mail for years, over them I have had some issues where I had to uninstall and re install to get some of the issues fixed. Most recently I had one of my 4 monitored mails stop polling in, but yet the other 3 all worked fine, so I uninstalled and re installed with no success? They are all aol emails on the pop setting and the other 3 work fine, and no issues, but my [removed email address to avoid spam] will not poll in. Any ideas?

Appreciate any help that you can give me… Rob