Feb 14 06:06:23 router-name kernel: systemd-journald[6099]: Failed to write entry (20 items, 667 bytes) despite vacuuming, ignoring: Bad message
These logs are not Junos reported log. This is something reported by the underlying kernel on the host.
It does seem to be a log message reported by journald on the kernel and indicates some problem in Journal file rotation on the host.For identifying the actual root cause underlying Host needs to be checked for any Storage issues.