iPhone 6 won't store emails

My iPhone 6 running of iOS 8.1.2 won't store all my flagged emails, 5 and only seems to remember 3 out of the 5. Until you actually search for the emails it can't be found by looking through inbox or updating. Restarting the phone does not do anything. This is also the case for regular emails where older emails seem to vanish until you search for them too. They are not stored in trash, junk or in archive. On settings I have checked that emails will not be deleted without asking first. Please help. Many thanks.