In a High Availability cluster on Basic Settings -> Date and Time the following message appears:
Slave is out of sync with the master
Due to a bug in ntp upstream the synchronisation of the slave node from the master may not work.
This can be worked around by forcing an ntp restart on both nodes.
systemctl stop ntp
systemctl start ntp
2. Log in to master's boot shell or local console and run this single command:
systemctl restart ntp
In around 10 minutes, the slave should get in sync with the master and the alert should disappear.
Note that you might need to repeat this procedure if the nodes get out of sync again.