In either case, that experimenter with Linux has no clue that they now have two time daemons running, one referencing an NTP server, & one referencing the host machine (which in the case of any recent host OS also does periodic checks against ntp servers), the two fight if there's a discrepancy.
Nor any clue that they should remove systemd-timesyncd (which they got as part of standard system utilities all unknowing), & not replace it with openntpd, ntpsec, or chrony (all that's available in Debian) without removing said additions.