Application Shortcut for Slack does not work

I've created an application shortcut for the "All Unreads" command in Slack to change from Cmd+Shift+A to Ctrl+Shift+A. ![Screenshot of the Application Shortcuts ][1] It shows up in the toolbar for Slack: ![Screenshot of the Slack toolbar ][2] When I press Ctrl+Shift+A in Slack, I see the "Go" toolbar header light up, but nothing happens. This is true for other toolbar entries in Slack as well, such as "Switch to Channel". How can I get application-specific shortcuts to work? Clicking the toolbar entry manually works, but it seems that activating it with a shortcut does not.