Custom Home Movie Posters

Here is the scenario:
I have created custom posters for my home videos. The custom posters show up in Plex on the PC but when accessing Plex through my Roku the Custom Posters are not shown. Instead the "Background" selected picture is shown (Only on the TV through Roku). If I replace the "Background" picture with the Custom Poster it will then show on the TV. Has anyone else experienced this problem?, and if so how did you fix it. I'm at my wits end. Thanks for your help.