I have a problem similar to the OP (which I'm not sure she responded was ever solved?).
I've had my iPad since June, and I was able to receive all email messages from my desktop, using Outlook, without problem, until a week ago. Now, after receiving email without problem for almost 5 months on my iPad, which is connected via WiFi on my home network, either I don't receive email on my iPad or only a few messages that I receive on my desktop also appear on my iPad.
Did I misunderstand that "IMAP" simply "duplicates" on your iPad what's been done on my desktop, e.g., if I delete the message on my desktop it's simultaneously deleted from my iPad, or does IMAP cause email messages to simultaneously appear on both the desktop and iPad?