Issue send / recieve suddenly on new account

Hi, I recently ( 4 weeks ago) added a new account to the client, all was working fine. then last week, I stopped seeing new emails in my inbox. I can send from the account, but these emails do not appear in my sent box. I have checked account settings and used teh diagnostics tab there to test and it tested OK, with green ticks and no errors reported…

Any ideas whats going on?