Hello I was having the same problem since I've gotten the 6 what was more confusing is that mainly only I seemed to be having the problem or so I thought. This problem seems to affect mostly people who upgraded from an older iPhone and has a strangely easy fix. I can't take credit for figuring out the fix "dmagdmag" over at the official apple forums seems to be the first to figure it out from what I've seen
The simple fix that has seemed to work this far is to
Go to Settings-->General-->Reset. Choose "Reset All Settings" and that will solve things.
This won't remove any data, media, ring tones, set up email accounts, text conversations, or third party keyboards. It fixed the problem for me and the minor inconvenience of going through the set up again and changing the ring tones and wallpaper took maybe ten minutes tops. I'm not sure if anyone is still looking for this fix but in case you are I hope it works for you