Discord recently moved to new GNOME tray icon system (I don't know what they call it technically in GNOME). so when you click on tray icon it has shell theme style menu instead of GTK 2 theme.
When Discord want to change the tray icon from normal to new message, it makes GNOME freeze for one second.
How can you reproduce the problem:
- Open Discord.
- Click on close to just have Discord icon in tray.
- Open a movie or just work normally with chrome or nautilus or any application.
Let the new message come in, so tray icon can change from normal to new message tray icon.
On changing to the new message tray icon, the system freezes for one second.
I don't know it's about Electron or Discord or GNOME.
This problem happening in Ubuntu GNOME 18.04.1 with GNOME shell 3.28.3.
I also tried XFCE just for this problem. didn't have this problem at all.