Maybe sometimes the log entry got delayed due to buffering. Try doing a sync, then check the log.
Using logger on my 68U (ASUS firmware) I've noticed a long latency before the message shows up in syslog. I've since added a couple sync commands and it seems better.
This seems strange since every Linux system I've worked on the log messages were explicitly flushed. But those were system library calls, not a stand-alone busybox program.