Run journalctl --since "1 days ago"
to see what systemd reports before that change happens.
Are you running containers on this server? For me, it seems to happen any time Kubernetes schedules a container on or off a node. That might happen hundreds of times per day, and thus these log messages are obnoxious.
Jun 10 08:38:24 docker01 containerd[1206]: time="2021-06-10T18:38" level=info msg="shim containerd-shim started" address="unix:///run/containerd/s/asdasasdasdasdasasdasd
" debug=false pid=122
Jun 10 08:38:25 docker01 systemd-networkd[719]: cali1234: Link DOWN
Jun 10 08:38:25 docker01 systemd-networkd[719]: cali1234: Lost carrier
Jun 10 08:38:25 docker01 systemd-timesyncd[94670]: Network configuration changed, trying to establish connection.
Jun 10 08:38:25 docker01 systemd-timesyncd[94670]: Synchronized to time server 10.11.12.13:123 (ntp01.example.org.nersc.gov).
Jun 10 08:38:25 docker01 systemd-timesyncd[94670]: Network configuration changed, trying to establish connection.
Jun 10 08:38:25 docker01 systemd-timesyncd[94670]: Synchronized to time server 10.11.12.13:123 (ntp01.example.org.nersc.gov).
This appears related to the two following bugs and appears patched in systemd v239. Ubuntu 18.04 ships with systemd v237 and is unlikely to receive a fix.