Celery beat does not work

**Describe the bug**
Celery beat is not run, no jobs are scheduled.

**To Reproduce**
Start the container with celery beat. See that no jobs get scheduled.

**Expected behavior**
Jobs should get scheduled.

**Screenshots**
N/A

**Additional context**
Previously, we had problems with calling `add_periodic_task` with WRONG kwarg `signature` instead of `sig.