Have the large gap on RRDGraph for all devices

Hi All,

I’m using LibreNMS for monitor the network devices are around 350 (Cisco switch/routers) the server runs on CentOS7 64 bit edition with 2CPU socket (6 cores/socket) 16GB of RAM.
LibreNMS working fine for a couple month until yesterday.
I’ve got the problem with LibreNMS rrdgraph shows the large gap for all monitored devices.
I’ve tried by following the performance tuning by enabling the rrdcached
and tuning the database with options below
innodb_file_per_table = 1
innodb_flush_log_at_trx_commit = 0
After tuning the graph can create with the closer gap but still not continue as before problem happened.
For the other function like the email alert when switch down or reboot, Event log work as normal.

Output from validate.php
bash-4.2$ ./validate.php

Component Version
LibreNMS 1.38-59-g052b9d1
DB Schema 247
PHP 7.2.6
MySQL 5.5.56-MariaDB
RRDTool 1.4.8


[OK] Composer Version: 1.6.5
[OK] Dependencies up-to-date.
[OK] Database connection successful
[OK] Database schema correct