hmmm, after twaking values, it appears the issue was caused by something on the vi client.

Rebooting the machine running the vi client resolved the issue.

Every ten minutes on esxi 3.5 it runs this script:

/sbin/decodeSel.sh which collects the ipmi data.

This is causing the performance data blanks.

So far my hypothesis has been soundly disproved:

Namedly the ipmi collection is causing the blank.

So i edited /var/spool/crontabs/root and commented out that collector line, then kill crond and restarted it

ps ax|grep crond.; kill pidnumber; crond -p

and the problem did not go away.

Now I think it is caused by the memory scanning.