Hi @MichiDahm,
this is expected behavior as you fetch up to 10 tasks. They will be handled sequentially in their handler. Each task takes 8 seconds and some milliseconds. So the 3rd task is unlocked before completion (locktime is 18 seconds) and is picked up in the fetch again.
My proposal to use maxTasks=1 and lockTime long enough to complete the task.
Then you can scale up starting additional workers for your topic.
Hope this helps, Ingo