shared album photos out of order

I created a shared album over 12 months ago, and just this morning have noticed that when viewing the photos at the web address (non-iPhone users) the photos are out of order. Photos taken and added a month ago are now at the top of the page and date stamped as being only a couple of days old.

I add photos to the album on the day I take them, can anyone explain how this has happened? They are still in the correct order in the album on my phone.