I was batch exporting some images from Lightroom and at the end of the Export I received a Dialog box saying there had been an internal Math Error on 1 of my images. The image itself was a copy so I thought maybe something was wrong with the copy. As I had made changes to the copy, I tried to Sync the Develop Settings to the original image. When I hit D for Develop, I received a blue image with a white x running through it. I could still execute the sync but It had no effect on the original version of the image. I then tried to sync the develop settings of another image (that didn't seem to have the problem of a blue image) and copy that to the original image and again no effect. It seems that this blue screen with x only is effecting 2-3 images out of the 400. I went to Preference>Performance>and deselected Use Graphics Processor but now the images effected are just black when I try to edit them in Develop and the Develop settings are all greyed out. Tried to contact Adobe support but they won't give me the option to chat. Any help would be greatly appreciated. I'm using latest version of Lightroom CC on a iMac retina 5k late 2014 i7 4GHz processor 32GB RAM AMD Radeon R9 295X 4GB
You may try and reset the Lightroom preferences back to default for the "Internal Math error" also, the images are showing black are you able to export those images out? because it's possible that the images are missing from Lightroom and you may need to relocate their locations in Lightroom.
Reset Preferences: Preference file and other file locations | Lightroom CC and 6
Relocate missing images: How to find missing photos in Photoshop Lightroom