Hi, try going out of Kodi and go to the setting (two cogs), now display and turn off Auto HDMI detection. Then underneath click on this to set the correct screen size...ie 1080 @ 60hz.
See if this helps.
When you go back to Kodi, when watching something press the ok on the remote. You should have the bottom sub menu up, go to the film reel icon and click on it. Near the bottom you have screen calibration, you can make some miner adjustments here too.
I normally move the line for subtitles up so its not in the black line of the screens aspect ratio wide screen.
After setting this go to the bottom and set as default.
Hope this helps...
Dave