I've recently discovered a potential bug in iCloud Photo Library - and I don't think it's a small one. Long story short, if you select the option "Disable and Delete" on a device using iCloud Photo Library, it will disable the service and begin a countdown from 30 days to permanently delete your photos - during that time you're able to re-enable iCloud Photo Library and stop the timer. What the bug seems to affect, however, is that if you re-enable it, it still counts down and deletes your stuff anyway. I disabled and deleted iCloud Photo Library around Jan 10, and enabled it again around Jan 12, however on Feb 10 is when I noticed my pictures were gone. I've opened a case with Apple Support who is working with their technical teams, but it's seriously frustrating because it seems like I'll have to wipe the iCloud Photo Library and upload my pictures AGAIN, after having done this last month already.