I was having some issues with iCloud Photo Library the other day. For some reason, about half of the images I had stored on IPL went from being regular, full-res images to compressed, low-res images. I have "optimization" turned on on my iPhone, so I'm guessing somewhere along the way the system got "confused" and replaced some of my full-res photos stored in the cloud with the "optimized" versions. Prior to this I was using IPL perfeclty fine for about a week - no issues. Fortunately, I also had all of my images stored in a Photo Stream. All of the images stored in my Photo Stream were exactly what they should be - full resolution. So, I went through and manually selected each of my 430 photos stored in my Photo Stream and downloaded them to my Camera Roll on my iPhone. Next, I went into iPhone Settings > iCloud > Photos, and disabled iCloud Photo Library. I selected to "Remove" all of the optimized photos. I then went into my iCloud Photo Library account via web browser, manually selected each photo, and deleted them all. Then I went into my iPhone Settings > iCloud > Photos, and enabled iCloud Photo Library. I selected the "Optimize" settings. All of the images from my Camera Roll uploaded to iCloud Photo Library. I did a check and the images that were showing as compressed in IPL are now full-res again. As a fail-safe I'm going to keep my Photo Stream enabled (for as long as Apple supports it and keeps it alive). I just don't trust IPL enough yet to rely on it to safely store all of my full-res images.