Thanks a lot for your help!!!
We performed below steps as we got approval and it worked.
service nagios stop
service ndo2db stop
pkill -9 nagios
killall -9 nagios
for i in `ipcs -q | grep nagios |awk '{print $2}'`; do ipcrm -q $i; done
service ndo2db start
service nagios start
It resolved the issue, the changes are getting reflected now. We were also not able to see any data in notifications, but after performing the steps, we are able to see it.
We re good to close the topic