If your alerts aren’t showing or displaying a black screen this could be due to your widget not being linked with your current “Scene Collection”. Don’t worry this is very simple to fix.
Linking your alert widget to the current scene
    1. On SLOBS, open the scene collection you’d like to use
    2. Head over to the Widget Themes page on Streamlabs
    3. Under “Scene Collections” select the widget theme you would like to use from the drop down menu
    4. Save your settings at the bottom of the page
    5. Ta da! Your alerts should now be linked and working. You can use the “Test widget” buttons to see if they work.