Alert on "users experiencing errors" not triggering, despite being over warning and error thresholds

### Environment SaaS (https://sentry.io/) ### Steps to Reproduce I haven't been able to reproduce this error since it happened, but I have the broken alert still in my account if that would be helpful. The alert settings are: When: Users experiencing errors is above 10 in 5 minutes Then: Send a Slack notification to <individual slack username> The query defined is ``` count_unique(user) (event.type:[error, default]) AND (level:fatal release.stage:adopted) over 5 minutes ``` ### Expected Result I should be getting Slack messages whenever the warning or error thresholds are exceeded ### Actual Result i'm not getting any messages. And the alert remains in a "resolved" state even though the timechart shows the counts being over threshold ### Product Area Alerts ### Link _No response_ ### DSN _No response_ ### Version _No response_