Batch sending error: jailshell Hangup

Hi, I regularly send upto 3000 subscribers via cronjob:
/home/myaccount/public_html/mysite/lists/admin/index.php -p processqueue -c /home/myaccount/public_html/mysite/lists/config/config.php > /dev/null 2>&1

It takes approx. 15 hours to send in batches of 30 e-mails every 5 minutes.
Tonight at 04:15 I received this message from cron daemon:
/usr/local/cpanel/bin/jailshell: line 1: 572943 Hangup /usr/local/bin/php
In the phplist eventlog the folllowing messages are missing
batch limit reached: 30 (30)
30 messages sent in #### seconds (#### msgs/hr)
Finished this run
There where no error messages in the log
At 04:20 the batch continued as expected.
Probably 30 subscribers did not get their newsletter.

Is this a known phplist 3.3.1 / Unix-Cpanel problem and what to do about it?

Thank you for your response
Best regards