I did some package updates on cloudservices1003/1003 and now icinga is complaining (wrongly) about NTP:
/home/andrew# /usr/lib/nagios/plugins/check_timedatectl Warning: NTP not enabled!
This is because these boxes are showing yet a new output format from timedatectl
root@cloudservices1004:/home/andrew# timedatectl
Local time: Thu 2020-03-05 18:09:59 UTC
Universal time: Thu 2020-03-05 18:09:59 UTC
RTC time: Thu 2020-03-05 18:09:59
Time zone: Etc/UTC (UTC, +0000)
System clock synchronized: yes
systemd-timesyncd.service active: yes
RTC in local TZ: noProbably we just need to update check_timedatectl (as @MoritzMuehlenhoff did a year ago) but I'm not yet clear on why this is happening just on those two (Stretch!) servers.