linux – Site does down every night at 01:15, 6K requests and high CPU usage [screenshots]

It’s been almost a week since we receive a site went down notification.

This site is built in PHP 7.2 and MariaDB, it is a legacy WordPress app that consumes a lot of ram and other resources, the response time on homepage: DOMContentLoaded: 2.40 s.

I have installed NETDATA on the server and uploaded some screenshots here:
https://imgur.com/a/TRp3FWI

PHP-FPM config:

pm.max_children = 100
pm.start_servers = 10
pm.min_spare_servers = 10
pm.max_spare_servers = 20
pm.max_requests = 500

Server (Dedicated vCPU Instance):

Intel Xeon Processor (Skylake, IBRS)
8 vCPU
32GB RAM

Any idea how to resolve this issue and what’s causing it?