Twice now I have run into the issue reported here:
https://support.google.com/chrome/thread/35897695?hl=en
where on rare occasions when I use the 3-finger swipe up/down gesture to see all open windows using the Mission Control feature on my Mac, all existing Chrome windows turn invisible. How do I get these windows to be visible again?
I was able to fix this by running the following command from Terminal:
killall Dock