Cancel button doesn't work

[TortugaAttack]

Description

If an experiment is canceled from the queue, the experiment seems to be removed, but if the platform is restarted, the canceled experiment is back again in the queue.

Reproducability

1. start experiment
2. start another expirement (so it is in the queue)
3. cancel second experiment
4. restart platform
5. Canceled experiment should be in the queue again (if not even executed right now)