This was what fixed it for me.
Using Ambari Version 2.7.3.0
SSH into host that's reporting stale alerts:
sudo vi /etc/ambari-agent/conf/ambari-agent.ini
change alert_grace_period (default 5 | change to: 15)
optional: restart service's instance reporting stale alerts (JournalNodes, NameNodes,etc)
sudo systemctl restart ambari-agent.service
Example using CentOS / Redhat