load-styles in admin provokes HTTP 503 error

[markhowellsmead]

Description

After updating anything - a plugin, theme or core - the load-styles.php path often results in an HTTP 503 error on several installations. The error occurs after the update, not during the update.

The hosting company has carried out extensive tests over several days and can confirm that these errors are either resolvable by reloading the path an irregular number of times in the browser, or by restarting PHP. No error message is displayed or logged. This results in the admin being displayed entirely without CSS.

The error appears to be occurring when 6.3 or 6.3.1 is in use.

Step-by-step reproduction instructions

See above.

Screenshots, screen recording, code snippet

No response

Environment info

WordPress 6.3 with no plugins. PHP 7.4 or 8 or 8.1. Apache server.

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[markhowellsmead]

According to extensive research and testing by the hosting company, the generation of the scripts compiled into the result of load-scripts.php requires in excess of 1Gb RAM. If the RAM limit is set to 512mb, regeneration of the assets after e.g. a plugin, theme or core update fails.

Setting CONCATENATE_SCRIPTS to false sometimes works around the problem, but this doesn't seem to be necessarily an ideal solution. (CONCATENATE_SCRIPTS is presumably set to true by default for a good reason.)

[markhowellsmead]

Closing in favour of https://core.trac.wordpress.org/ticket/57548. The problem is not resolved, though.