For What Its Worth:
I do have same annoying
logstash/async.go:256 Failed to publish events
caused by: read tcp 192.0.2.3:59058->192.0.2.4:5044: i/o timeout
error.
In ERROR logstash/async.go:256 Failed to publish events caused by: write tcp 10.XXX.XX.XX:43522->10.XXX.XX.XX:5044: i/o timeout 2019-08-06T16:04:30.967+0800 ERROR pipeline/output.go:121 Failed to publish events:IOtimeout is it also reported (and closed after 28 days)
Pointers on what to check (journalbeat side or the logstash side) are welcome.