[Observium] graph is not include some section

Hello, as you see in attachment i see my graph for all ports is not include some section and it has some are that are white and data is not available for those time period. can any one help me why this happen? also i use latest version of observium. i guess maybe it was for cronjob that take about 1-3 minutes for run poller. is it correct or any other idea? thanks,