Photos 'missing' in iCloud Photo Library - showing as blank with small Cloud icon
I have my iPhone 6, my MacBook Pro and my iPad all using iCloud Photo Library - and while all new images sync seamlessly, there are several hundred dotted through my library that only appear as blank with a small cloud icon. They exist on the iCloud.com website when I log in, but do not seem to have propagated to my devices properly - but it is not showing as awaiting sync or anything. It has been like this for weeks. Any ideas how to force a re-sync?
I have my iPhone 6, my MacBook Pro and my iPad all using iCloud Photo Library - and while all new images sync seamlessly, there are several hundred dotted through my library that only appear as blank with a small cloud icon. They exist on the iCloud.com website when I log in, but do not seem to have propagated to my devices properly - but it is not showing as awaiting sync or anything. It has been like this for weeks. Any ideas how to force a re-sync?