Heloo :) When I left click on a some apps in systray, the application won't open it's main window. This is a problem since a few versions ago and is very uncomfortable. For example if I want to open Skype, I have to right click on the Skype icon and select Open Skype. Left click just does nothing - single or double click. The same applies to applications like Discord, Viber, etc. I tried to open this apps with left click on Cinnamon, LXDE, Xfce and there isn't such problem at all. It's definitely a Plasma problem.
*** This bug has been marked as a duplicate of bug 365308 ***