to see alerts in Alert Manager, you have to configure all your alerts as Global, otherwise you don't see in this App.
If you found some error in JS execution, there's a message that you can find on the GitHub site.
Al the alerts are in global.
I can see al the alerts on the dashboard. What I cannot do is to filter them. If I choose to just see the ones with new status, it still show me all the alerts. In this example I select to just see critical alerts in the las 24 hours but it still shows me all alerts of the last 24 hours.