It's finicky. Particularly these days. Game lag is prevalent too.

Double-click and give it a few seconds.

Triple-click, whatever, just keep pounding on it until you see it open. It will probably close soon after (catching up with your clicks), but you'll at least know it's working. After that, double or triple clicks might start working for you. Such has been working for me.

It's like it's forgotten it has that ability / code, and the clicking gets it to try again. And the game lag means when it calls to the server to get all current messages ... it can take some seconds.

GL&HF