I've installed the Slack snap; recently, its tray icon stopped displaying. Instead there's just a blank space – though if I right-click it, the Slack menu still opens. All my other tray icons are working fine.
Why has Slack's icon disappeared, and how can I get it back?
I'm using i3 with i3bar to display tray icons, on Ubuntu 18.04. Slack is currently at version 3.3.7.