[v8.4.0] alert number is not as expected when using variables

[EnyaWong]

Question and Steps to reproduce

Question and Steps to reproduce
当使用变量的时候，告警数量不符合预期。
在配置告警规则，如果使用变量（比如application, 枚举值3个：aiwing-facade-app-middle,aiwing-facade-app,aiwing-facade-app-ai）

告警promql:
sum by(instance, application) (rate(http_server_requests_seconds_count{application="$application", uri="/check"}[1m])) > 0

问题：
aiwing-facade-app-middle对应有2个instance，aiwing-facade-app对应有2个instance，aiwing-facade-app-ai对应有2个instance
/chek接口每30s请求一次
那么预期会收到6个告警，但是实际上只收到3个告警。

Relevant logs and configurations

无

Version

v8.4.0