Live TV thumb & background problem

Just upgraded to Kodi 17.1 from google play store and have Titan 3.7.56. I’m using a MythTV backend. I’ve selected PVR Random Thumb and when the menu is generated, one of the recorded programs shows. But when the thumb changes to the next program, it’s blank. I suspect one of my recordings has no graphics, but I’ve gone into the helper app and specified the titles that should be ignored for artwork with no success. Any suggestions?