hook_cron_queue_info stopped
If you are sure that your execution do not produce programming errors, the problem may come from the fact that Drupal only executes queue items when running Cron. Taking into account that Drupal Cron is limited by time and PHP memory, your queue items may not be fully processed in a single Cron run.

You can refer to this issue I created some time ago about a very similar problem.

In short, I solved it by processing queue items every X minutes.