Yay, another subtle combination of @vaceletm and @tgerbet work that lead to... intresting results.

The former reworked the cron management to be able to better control the background processing of tasks.

The later fixed a wrong behavior of workers themselves to avoid working on stalled data  (request #13666).

When you combine both the workers are sending commands (with tuleap.php) that are delayed (because workers are started by tuleap process-system-event that is in cron that have TLP_DELAY_CRON_CMD. The environment variable is duly propagated all the way down to `tuleap queue:task-worker-process` that quitely wait for the random delay to execute the worker duty.

Computer Science is Hard(c)(tm)