[Observium] Polling missed?

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?