My Cloud Backup for iOS not backing up all files

[phm66]

I have setup My Cloud on my iPhone 6s and enabled auto-backup for photos and videos. The synchronisation seems to work at the start and if i look at the activity it syncs 57 images until it says it has completed. However there are far more than 57 images on my phone and no matter what I do (turn on/turn off) auto sync the app will only sync the most recent 57 images on my phone. There are currently several hundred images that i want to sync across but for some reason it won’t copy all of them. I know that the app need to be left running in the foreground and that the lock screen will prevent it from syncing but i have tried all this and still I am unable to sync all the photos. Any ideas on how to resolve this?