Flat areas in system statistics

From time to time system statistics remains flat for a while in CPU utilization and System statistics, Email messages section show normal graphics. Raw dato shows same digits every five minutes. Restarting web min does not solve the problem. My system is Centos 6.7 Webmin version 1.760, Virtualmin version 4.18 The issue began on august 21h (see attached screen shot) Any suggestion?

TKS

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A flat area typically means that either the system was down during that period, or that Cloudmin was unable to contact it. Did the status of these systems change at that time?

The system is running fine, mail section graphs shows no interruptions. at all . In attached screenshot you can see the system is delivering mail even when cpu load is flat.

Also "Historic System Statistics" (Webminstats 2.12 module by gerbier) shows no flat areas during same period of time (see 2nd attached screenshot)

BTW I don't use Cloudmin.

Is it only the CPU load stat that goes flat, or do others as well?

Mail section shows normal activity with no flat areas. Please see my first post where I explain which graphs are showing flat areas. Also have look to the screenshots I attached. The problem appears randomly.

What about the 5 and 15 minute load averages, and the percentage of CPU used - are they also flat in Virtualmin at the same time?