Alertmanager does not fire alarm

Question

I use the following config for alertmanager of AWS Prometheus, and it works:

alertmanager_config: |
  global:
    resolve_timeout: 60s
  route:
    receiver: default
    group_by: ['alertname']
    group_wait: 10s
    group_interval: 5m
    repeat_interval: 1h
  receivers:
    - name: 'default'
      sns_configs:
      - topic_arn: <arn>
        sigv4:
          region: <region>

But when i added another sns topic, no alert was sent while there are many alarm fired

alertmanager_config: |
  global:
    resolve_timeout: 60s
  route:
    receiver: default
    group_by: ['alertname']
    group_wait: 10s
    group_interval: 5m
    repeat_interval: 1h
    routes:
    - match:
        severity: critical
      receiver: all_channel
  receivers:
    - name: 'default'
      sns_configs:
      - topic_arn: <new SNS arn>
        sigv4:
          region: <region>
    - name: 'all_channel'
      sns_configs:
      - topic_arn: <old SNS arn>
        sigv4:
          region: <region>

Right after i changed back to the old config, the alerts fired. Anyone know what's wrong with the new config? Big thanks.

I tried amtool syntax check and it passes the check.