Photo's in Camera Roll are out of chronological order

I've just backed up my 5s and restored it to a a new 6s. When I look in the camera roll the first photo (at the top) is dated 26th of September 2014. If I scroll though about 2 thirds of the way down I get to the photo I took today. The next photo is dated 2nd March 2008 and then if I keep scrolling down the very last photo (at the bottom) is dated 24th of September 2014.

It's like the first third of my photos have been put after the 2nd third. Very frustrating conssidering I have over 4000 pictures.

If I open the camera roll from within an app like Whatsapp the order is correct.

How can I rectify this??