intermittent Graph

We monitor 200 more devices, mostly cisco, but I have a broken graph problem broken,
I Use the device:
12 Cpu, with 16Gb of RAM

  o Linux OS 4.4.0-87-generic [amd64] (Ubuntu 16.04)
  O Apache 2.4.18
  o PHP 7.0.22-2 + ubuntu16.04.1 + deb.sury.org + 4 (OPcache: DISABLED)
  O Python 2.7.12
  o MySQL 5.7.19-0ubuntu0.16.04.1 (extension: mysqli 5.0.12-dev)
  SNMP NET-SNMP 5.7.3
  O RRDtool 1.5.5