Icons disappearing from cmd+tab application switcher When using my MacBook for a while (Sierra, 10.12.3) then using cmd+tab to switch applications, I sometimes lose application icons. In the screenshot below, it's limited to Chrome but multiple applications will disappear at a time.

I can get the icons back temporarily by restarting or running killall -KILL Dock but I'd like a more permanent solution.
I had the same issue, and after restarting Dock, I still couldn't see the app icons popping up when I pressed cmd-tab. However, if you could see the Dock restarted after following the instructions to restart it, then the problem might be your external monitor. Unplugging the video cable to my external monitor and plugging it back in fixed it for me.