Kodi converts interlaced media for progressive output by doubling the original refresh rate and rendering each half-frame in its own full frame, e.g. PAL 1080i @ 25fps media becomes 1080p @ 50fps, and NTSC 1080i @ 29.97 becomes 1080p @ 59.94fps. For this rate doubling to work, we need to ensure the whitelisted 1080p modes do not contain 1080p @ 25/29.97/30Hz rates, else Kodi will see an exact match against resolution and refresh rate and you will see high CPU loads and 50% of frames being dropped. If the modes are removed, Kodi will use 50Hz/59.94Hz rates, and if the media is interlaced, Kodi can still render 100% of the frames.