I checked the php-fpm log. It reports the following, so I'm going to take action on this:

[18-Dec-2024 00:13:32] NOTICE: fpm is running, pid 36133
[18-Dec-2024 00:13:32] NOTICE: ready to handle connections
[18-Dec-2024 00:13:32] NOTICE: systemd monitor interval set to 10000ms
[18-Dec-2024 00:15:08] WARNING: [pool example.site] server reached pm.max_children setting (2), consider raising it
[18-Dec-2024 00:36:31] NOTICE: Terminating ...
[18-Dec-2024 00:36:31] NOTICE: exiting, bye-bye!
[18-Dec-2024 00:36:31] NOTICE: [pool example.site] pm.start_servers is not set. It's been set to 1.