wordpress benchmark shows very unstable with mariadb 10.4.x

when running wordpress benchmark with https://gitlab.devtools.intel.com/DCSP/HHVM/oss-performance-php, the result is fluctuating from 200 to 4600, this problem does not exist on 10.3.17.

Details:
wordpress transaction rate

Env:
ubuntu 19.04
php7.3
siege 4.0.4

Steps:
git clone the workload from https://github.com/facebookarchive/oss-performance and set up through below steps:
$cd oss-performance-php
$wget https://getcomposer.org/installer -O composer-setup.php
$php -r "if (hash_file('sha384', 'composer-setup.php') === 'a5c698ffe4b8e849a443b120cd5ba38043260d5c4023dbf93e1558871f1f07f58274fc6f4c93bcfd858c6bd0775cd8d1')

{ echo 'Installer verified'; }

else

{ echo 'Installer corrupt'; unlink('composer-setup.php'); }

echo PHP_EOL;"
$php composer-setup.php --disable-tls
$php composer.phar install
$php perf.php --wordpress --php=/usr/bin/php-fpm (Note: update the path to the php-fpm on your machine)

And get result as below, Siege RPS:
{
"Combined":

{ "Siege requests": 277358, "Siege wall sec": 0.04, "Siege RPS": 4625.72, "Siege successful requests": 264034, "Siege failed requests": 1, "Nginx hits": 277578, "Nginx avg bytes": 30166.824334061057, "Nginx avg time": 0.04225272896268245, "Nginx P50 time": 0.042, "Nginx P90 time": 0.057, "Nginx P95 time": 0.062, "Nginx P99 time": 0.072, "Nginx 200": 252279, "Nginx 502": 1, "Nginx 301": 11943, "Nginx 404": 13355, "canonical": 1 }

}