Alertmanager sending duplicate notifications after 'resolved' notification when running with multiple replicas

What did you do?
I have VM (Victoriametrics) Alert running with Alertmanager, with 2 replicas each. I am ingesting the metric disk_usage with value > threshold value. As soon as I receive an email from alertmanager (which is after 20 minutes in my case, see below files), I am stopping the data ingestion, which stops the alert breach as well.

• VM_rules.yaml

groups:
- name: test_group
  interval: 5m
  concurrency: 1
  rules:
    - alert: High Disk Usage
      expr: ((avg(disk_usage[5m]) by (instance)) > 95)
      for: 15m
      labels:
        severity: critical

• alertmanager_config.yaml

global:
  resolve_timeout: 5m
  smtp_smarthost: smtp.gmail.com:587
  smtp_auth_username: XXX
  smtp_auth_password: XXX
  smtp_from: XXX@ABC.com
route:
  group_by: [alert_id, instance]
  receiver: test-default
  group_interval: 5m
  repeat_interval: 12h
receivers:
- name: test-default
  email_configs:
  - to: XYZ@ABC.com
    send_resolved: true 

What did you expect to see?
Alertmanager should send a 'fired' notification and a 'resolved' notification after I stop data ingestion because breach is stopped.

What did you see instead? Under which circumstances?
Alertmanager sends a 'fired' notification, but when the ingestion/breach is stopped, it sends a 'resolved' notification along with another 'fired' notification. And, 'resolved' email for this duplicate 'fired' email comes either instantaneously or in the next group_interval. Also, sometimes I see arbitrarily multiple pairs of duplicate 'fired-resolved' mails even after breach is stopped.
This unexpected behaviour is seen only when alertmanager is running with multiple (>=2) replicas.

Environment

• Alertmanager version:
  v.0.27.0

Start by reproducing the behavior with VM_rules.yaml and alertmanager_config.yaml using two Alertmanager replicas, then compare the fired and resolved notifications after ingestion stops. Done means the configured setup sends one fired notification and one resolved notification, without duplicate pairs or extra notifications.