apache – My WordPress website encounters the white screen of death for an unknown reason, but it is fixed after restarting the server.

The problem we are facing is very new to us. We have never experienced this before with our website or with our web server (in the last 8 years). Just recently, for 2 weeks, we have this problem and it happened more than 3 times.

description of the problem

Our site knows "the white screen of death". We do not see any error. Please see the screenshot for better understanding. it's just that. The site is just trying to load but can not.

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Findings: what we did to solve this problem

We can fix it (temporarily) if we reboot the server (restarting the entire virtual machine).

But this is not a viable solution. Since we have other WordPress and non-Wordpress websites on this server, this problem does not exist. And restarting the server means that all server sites are down for 5 to 10 minutes. After the reboot, the server site comes back and works normally.

But this problem has occurred at least 3 times since last week. We can not reproduce the error by clicking on a page. There is no particular moment of the day when this happens.

More information

The only significant change we can think of is upgrading the PHP version of the site from version 5.3 to version 7.2 on our web server. For your information, we updated the version of PHP last month. And for about 3 weeks, we did not see that or any other problem. The wordpress version of the site is 4.9.1

We tried to check the error log at the time of the problem. but we did not find anything relevant. This is the error that we could see in the error log. Although I did not think that was the problem but I corrected the SQL query mentioned in the error log. But we have faced the same problem again today.

[Tue Apr 23 13:48:35 2019] [error] [client]    FastCGI: server "/var/run/psychicf-remi-safe-php72.fcgi" stderr: PHP message: WordPress database error You have an error in your SQL syntax; Consult the manual for your MySQL server version for syntax to use near "ORDER BY number DESC". in line 1 for the query SELECT * FROM view_site_numbers WHERE campaign_id = "7" AND `use` =" PPC "LIMIT 2 ORDER BY DESC number realized by require (wp-blog-header.php & # 39;) , require_once (& # 39; wp-includes / template-loader.php & # 39;), include (& themes / psychicFuture / css / content-all-horoscopes.php), get_header, location_template, load_template, require_once (& # 39; / themes / psychicFuture / header.php), do_shortcode, preg_replace_callback, do_shortcode_tag, get_prs_number_register, referent: https://thehoroscopejunkie.ca/weekly_horoscopes.html

I do not know where to look. Can you please advice?