Out of curiosity, where would I begin looking for any issues with missed polls or graphs not showing data for a certain period of time?  I have looked under /var/log and do not see anything that stands out.  I'm not sure if there are any other locations i can investigate this on.  I am running ubuntu server 12.04.3 LTS.  Attached are a couple of graphs you can see the gap of data not presented, or possibly missing?  The weird part is, i have about 90% of my devices that show this gap, but the other 10% doesnt.  Theres no specific network device/factor that would be have created this either.  Any thoughts/suggestions/ideas?