php-fpm process receiving SIGKILL signal in Kubernetes
You have a very low memory limit considering you want to run multiple PHP processes inside managed by php-fpm. It is very likely that your processes are killed due to this memory constraint. I would advise switching memory limit to something like 400Mi and checking again.
Following error showing on Kubernetes pod, increased the php-fpm memory limit it helped
php_admin_value[memory_limit] = 200Mphp-fpm Error log
api-service-php-fpm [17-Aug-2021 09:14:23] WARNING: [pool www] child 51 exited on signal 9 (SIGKILL) after 179.524183 seconds from start api-service-php-fpm [17-Aug-2021 09:14:23] NOTICE: [pool www] child 57 started