My cron job to process the mailing queue manually used to work fine, until yesterday when I upgraded from 3.3.7 to 3.6.10. I created a mailing and set it ready into the queue to be sent. From Parallels Plesk I started the cron job. I always send batches of 90 mails and then about 1 minute after the success-message I start the next batch. The first 90 mails were sent succesfully, however when I started the cron job for the second batch, it ended with an error saying:
Het voltooien van taak “httpdocs/…/lists/admin/index.php” is geslaagd in 2 seconden. Uitvoer:
phpList - phpList version 3.6.10 (c) 2000-2022 phpList Ltd, https://www.phplist.com
phpList - Op deze pagina is reeds een proces actief 82 seconden geleden
phpList - Commandline wordt uitgevoerd, huidige actie gestaakt. Bij de volgende actie zal duidelijk worden wat er gedaan moet worden.
Translated into English:
Completing task “httpdocs/…/lists/admin/index.php” succeeded in 2 seconds. Output:
phpList - phpList version 3.6.10 (c) 2000-2022 phpList Ltd, https://www.phplist.com
phpList - This page already has a process running 82 seconds ago
phpList - Commandline in progress, current action aborted. The next action will make it clear what needs to be done.
I’m not really sure where or what the problem is. It looks like the task is hanging or so. Something in phpList or something server side?
/edit. This morning I was able to start the 2nd batch. So apparently the system holds the task busy somehow and releases it the next day or so. But which part of the system that is I have no clue. The problem is now occuring in the 3rd batch 
