Some artwork not showing on home sharing library

PC running Windows 7 has all of our movies and TV shows. Home Sharing iTunes is running. We have 2 iPads and 4 iPhones that we share this library on. It doesn't matter which device we use, some of the artwork for the movies and shows do not show up. I have deleted the artwork for some of the ones that don't show and re-attached using iTunes, that did not work. I have deleted the artwork cache, that didn't work. All of this didn't start happening until IOS 8. I have been trying to fix this issue forever, any help would be appreciated.