External monitor not sending traffic on configured interval

Hi all, After some time of investigating an issue, I got to the point when I need to ask for some extra opinion!

Basically I have an external monitor running every 30s, it's a ftps through curl command connecting to backend file server to check for existence of specific file. I have this service configured on 3 different LTM pairs and there is no issue with it.

However on one particular LTM I noticed that monitor randomly runs on different intervals. When I enabled Monitor Logging I can see that F5 attempts to run the monitor every 30s, however when I run tcpdump I can see that there is no traffic being sent sometimes.( sometimes it run every 1min, sometimes after 90s etc) This point doesn't make sense to me.

When I manually initiate the health monitor file with "sh -x" command via CLI, it always works and I get expected response. Just to add, when using other bigip monitors, there is not issue noticed as yet.

Appreciate any pointers on how to further troubleshoot this issue. Have a case with F5 however as this is external monitor , they do not support it. I am curious on why i can't see traffic being initiated from F5 device as per config?

I'm running V12.0.03.0.654.

See below the logic of the monitor:

IP=

echo ${1} | sed 's/::ffff://'

PIDFILE="/var/run/

basename ${0}

if [ -f $PIDFILE ] then

kill -9

cat $PIDFILE

rdexec 1 curl --cacert /config/filestore/files_d/Common_d/certificate_d/certfile -k --ftp-ssl @${IP}:${PORT} -l --silent | grep "MONITOR.txt" 2>&1 > /dev/null

if [ $? -eq 0 ] then echo "UP" fi rm -f $PIDFILE exit