[Mailmunge] No route to host Error

[list at ptld.com]

Any idea what might cause this?

  Mar  8 03:19:12 host mailmunge-mx[908166]: 4KCSsK2Vx6z4l3jt: Worker 0 stderr: connect: No route to host
  Mar  8 03:19:22 host mailmunge-mx[908166]: 4KCSsK2Vx6z4l3jt: Worker 0 stderr: connect: No route to host
  Mar  8 03:19:22 host mailmunge[908172]: 4KCSsK2Vx6z4l3jt: Filter time is 21396ms

Normal filter run time is between 8ms to 100ms
This same sender (spammer) attempted minutes before and was given a temp fail

  Mar  8 03:15:59 host mailmunge-mx[908166]: Killing busy worker 0 (pid 908226) req=366 age=979701 req_age=979591: Busy timeout
  Mar  8 03:15:59 host mailmunge[908172]: 4KCSnD60s3z4l3lK: Error from multiplexor: ERR Filter timed out - check filter rules or system load
  Mar  8 03:15:59 host postfix/cleanup[1102541]: 4KCSnD60s3z4l3lK: milter-reject: END-OF-MESSAGE from xvfrptcc.outbound-mail.sendgrid.net[168.245.55.204]: 4.7.1 Service unavailable - try again later; ...
  Mar  8 03:15:59 host mailmunge-mx[908166]: Reap: worker 0 (pid
908226) exited due to SIGTERM/SIGKILL as expected.
  Mar  8 03:15:59 host mailmunge-mx[908166]: Worker 0 resource usage: req=366, scans=183, user=14.219, sys=0.912, nswap=0, majflt=0, minflt=105957, maxrss=27380, bi=0, bo=16192
  Mar  8 03:15:59 host postfix/smtpd[1102530]: disconnect from xvfrptcc.outbound-mail.sendgrid.net[168.245.55.204] ehlo=2 starttls=1 mail=1 rcpt=1 data=0/1 quit=1 commands=6/7
  Mar  8 03:16:00 host mailmunge-mx[908166]: Starting worker 0 (pid 1102583) (2 running): Bringing workers up to minWorkers (2)

I see nothing else in the logs to indicate what might have been happening to cause something to hang and timeout.
After this incident additional mail was received as normal with ~ 10ms filter times.
Any tips on what i can do to get better insight into what is causing the filter to hang?
Any idea which part of the munge process had the connect no route error and what was it trying to connect to?