iCloud Photo Library, the photo-syncing system by Apple, is known to make changes to your photo library that may cause issues within Mylio. Users who have turned on iCloud Photo Library’s “Optimize” option have reported compatibility issues ranging from error messages to black squares in place of images to duplicates across their devices.
It is recommended at this time that you do not use Apple’s iCloud Photo Library in conjunction with Mylio while we investigate these issues and ensure that your Mylio photos and library will not be altered.
Update (March 9th, 2018):
We are actively working on this issue and hope to have an announcement soon.