LibreNMS not show the host down

Hi,

I’m using the LibreNMS with CentOS 7 it working with expected until 2 week ago I have noticed that the server not show the host down in WebUI and also not email alert. After checked the device graph it have no data in the down period.
I’ve run everything on single server with 12 core CPU+16GB RAM + 500GB HDD
I’ve 400 devices and 19xxx interfaces.

below is my validate.php

bash-4.2$ ./validate.php

Component Version
LibreNMS 1.48.1-64-g9dba9f6
DB Schema 2019_01_16_195644_add_vrf_id_and_bgpLocalAs (131)
PHP 7.2.10
MySQL 5.5.60-MariaDB
RRDTool 1.4.8
SNMP NET-SNMP 5.7.2

====================================

[OK] Composer Version: 1.7.2
[OK] Dependencies up-to-date.
[OK] Database connection successful
[OK] Database schema correct
[WARN] Some devices have not been polled in the last 5 minutes. You may have performance issues.
[FIX]:
Check your poll log and see: http://docs.librenms.org/Support/Performance/
Devices:
10.xx.yy.244
10.xx.yy.173
[FAIL] Some devices have not completed their polling run in 5 minutes, this will create gaps in data.
[FIX]:
Check your poll log and see: http://docs.librenms.org/Support/Performance/
Devices:
10.xx.yy.173
10.xx.yy.40
10.xx.yy.35
[FAIL] Discovery has not completed in the last 24 hours.
[FIX]:
Check the cron job to make sure it is running and using discovery-wrapper.py
bash-4.2$ ^C
bash-4.2$

And my cron.d/librenms is below.

cat /etc/cron.d/librenms

# Using this cron file requires an additional user on your system, please see install docs.
33 */6 * * * librenms /opt/librenms/cronic /opt/librenms/discovery-wrapper.py 16
*/30 * * * * librenms /opt/librenms/discovery.php -h new >> /dev/null 2>&1
*/2 * * * * librenms /opt/librenms/cronic /opt/librenms/poller-wrapper.py 100
* * * * * librenms /opt/librenms/alerts.php >> /dev/null 2>&1
*/5 * * * * librenms /opt/librenms/poll-billing.php >> /dev/null 2>&1
01 * * * * librenms /opt/librenms/billing-calculate.php >> /dev/null 2>&1
*/5 * * * * librenms /opt/librenms/check-services.php >> /dev/null 2>&1
# Daily maintenance script. DO NOT DISABLE!
# If you want to modify updates:
# Switch to monthly stable release: https://docs.librenms.org/General/Releases/
15 0 * * * librenms /opt/librenms/daily.sh >> /dev/null 2>&1

Anyone ever have the same issue? Please share the idea how to resolve the problem
Thank you in advance.