I downloaded and converted to DNG a flash card full of images. They a;; appear along the bottom panel but I can only bring the first one up onto the screen. As I highlight others down the line they highlight but will not pop up onto the screen. Grid mode works fine but makes the process much more difficult. When I change to develop mode I can now advance and bring images onto the screen, mark as rejected, etc., although I cannot flag favorites or rate them. This has never happened before.
First step, try resetting the Preferences file. Resetting Preferences in Lightroom CC/6
Are the RIght/Left arrow keys not working also?
Also if you are only rating, flagging, labeling, the photos- using Loupe View [E] in the Library module may be a better (and faster) option.
Actually, I had not tried simply restarting LR. When I did my problem cleared. Why I did not try that first I do not know. Thank you.