I get this off and on with Yahoo! mail but its not due to 9.0 specifically. Over the years I have had the service come and go but have stuck with it and waited it out. You could try removing the account from your device and adding it again. That helps at times. Honestly though, you wait. When mine stops working correctly its not just my phone, its my iPad too so I have to believe its not device specific if its quitting on two devices at the same time.