The Journal beat service appears to stop ending log events after the journal is rotated.
-rw-r-----+ 1 root systemd-journal 16M Dec 13 13:10 system@662da6c735c64e5f98db920498125e8e-0000000001f1a3dc-00057ce953492eca.journal
-rw-r-----+ 1 root systemd-journal 8.0M Dec 13 13:47 system.journal
The last journalbeat log events happened about the same time:
|2018-12-13T13:10:57.612-0500|INFO|[input]|input/input.go:131|journalbeat successfully published 8 events|{"id": "513e85da-8030-4a17-91d7-908bb09759ab"}|
|---|---|---|---|---|---|
|2018-12-13T13:11:00.614-0500|INFO|[input]|input/input.go:131|journalbeat successfully published 2 events|{"id": "513e85da-8030-4a17-91d7-908bb09759ab"}|
This is on Ubuntu 16.04 with no explicit settings in the journal.conf file.
EDIT
The journal files referenced above are located /run/log/journal/~machine-id~