HTTP ERROR 500 after running ./ and ./validate.php

$ ./validate.php


Component Version
LibreNMS 1.49-32-g8d67bb7
DB Schema 2019_02_10_220000_add_dates_to_fdb (132)
PHP 7.2.16-1+0~20190307202206.17+jessie~1.gbpa7be82
MySQL 10.0.38-MariaDB-0+deb8u1
RRDTool 1.4.8


[OK] Composer Version: 1.8.4
[OK] Dependencies up-to-date.
[OK] Database connection successful
[OK] Database schema correct
[FAIL] Some devices have not completed their polling run in 5 minutes, this will create gaps in data.
Check your poll log and see:

How to troubleshoot ?

Check your librenms.log.

Recently people have been getting this when they update PHP, but their webserver is still running the old version of PHP.