I have had success fixing this issue... For my iPhone 6 plus anyway! Hopefully it will work for you too!
What finally worked was backing up my phone to icloud (contacts photos etc) do this by making sure you are connected to wifi then go to settings>icloud>backup>backup now
then plug the phone into the computer and go to iTunes and click on restore iPhone.
This may take a little while to download the software etc but slowly but surely...
Once it it has finished restoring choose set up as new phone.
On the phone set upas you would any new phone and make sure you sign into iCloud -all your photos and contacts should be there.
I initially tried restoring from a full backup from my computer instead of setting up as a new phone and that did not work.. Same thing happening. Must be whatever went weird on the phone goes back on when you use your backup. I have a suspicion that the error may be due to photo apps I installed... But I can't say for sure.. For now I've left them off and going to see if the problem is fixed 100% then try to put those apps back on and see if it starts up again. Probably because the apps haven't been optimised for ios8 yet.
ALSO as side note ; BEFORE YOU RESTORE; you may notice that when you connect your phone to the computer and go to iPhoto and import your pictures all the pictures you can't see in photos on your phone will appear on your computer...
Good luck! if you have success with this it would be good maybe to post back so others can see that it worked for you too and give it a try... It's such an annoying problem!
🙂