Issue PHP Message - a Job is already running

[Mirko1212]

Hello,

I have a Virtual Server with Debian 8.9 and Plesk 17.5.30 and I find an unusual problem.

On this Virtual Machine is configured a subscription (xxxxx.com) and within it several additional domains such as (yyyyy.com and zzzzz.eu)
All domains have been configured with PHP-FPM and Apache, this is the php.ini that I configured by adding it to /var/www/vhosts/system/xxxxx.com/conf/php.ini:

[php-fpm-pool-settings]
pm = ondemand
pm.max_children = 10
pm.start_servers = 1
pm.min_spare_servers = 1
pm.max_spare_servers = 5
pm.process_idle_timeout = 10s
pm.max_requests = 500

every night at 1:20 the system create a process that is always running.

root@vps: ps wwauxf | grep xxxxx.com

xxxxx 10048 0.0 0.3 577480 52776 ? S 01:20 0:00 \_ php-fpm: pool xxxxx.com

in the file /var/log /php5-fpm, this warning is generated every minute:

[18-Oct-2017 13:12:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:13:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:14:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:15:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:16:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:17:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:18:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:19:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:20:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:21:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:22:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"
[18-Oct-2017 13:23:08] WARNING: [pool xxxxx.com] child 10048 said into stderr: "NOTICE: PHP message: A job is already running"

What could it be?
Thanks

Kind Regards.
Mirko