Kibana dashboard issue - i have created a disk usage dashboard , it doesnot show up a straight line --but with dotted lines

Elastic Stack Kibana
1

ELK - 7.17.3 , KIBANA 7.17.3
I have a 3 node cluster and two logstash server and one kibana server

I have created disk usage dashboard , but it shows the data in dotted line for 15 minutes or 30 minutes.. while for 1 hour period it shows a straight line

It looks like it is missing data for 15 or 30 mintues.. how could i have this issue resolved

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2

In this dashboard, i can see the cpu lines are pretty clear.. while the disk utilization lines are dotted