Very slow UI on Krypton 17.0 release

I built the Kodi 17 Krypton release on a Raspberry Pi 3, yet when I start it up, it the user-interface is very slow. It takes several seconds to navigate from one button to another. My Pi has tons of free RAM, and I made it use 256 MB of video memory in the /boot/cmdline.txt (setting gpu_mem=256).

How can I speed up the UI?