What you were expecting to happen, and what actually happened?
I was expecting to see the newest chat messages popping in while on the world map screen. I’m actually seeing messages from a few hours ago popping in, in a never ending stream. Going by some interspersed guild messages they seem to be in chronological order, without anything missing. On a wild guess, I suspect the new Unity client receives messages even when another application is currently active, buffers all of them and starts the display loop once you tab back to Gems of War.
What are the steps to make it happen again?
Go raiding in some other MMORPG, tab back to GoW whenever the raid is waiting for cooldowns to do a boss fight.