Adding task to published data donation study may hang running donations

[TjerkNan]

Describe the bug
When you add a task in the workflow of a published data donation, that extra step will immediately show up during a data donation. However, if the participant selects this step during the donation started before this step was added, the step hangs indefinately.

I think I discovered this issue by accident and I'm making the assumption it's not Debian specific.

To Reproduce
Steps to reproduce the behavior:

1. Publish a data donation study
2. Start a data donation and keep it open
3. Add a data donation step
4. Observe the new step in the donation window
5. Try to click on the new step and start it

Expected behavior
New step works immediately or we don't allow modification of published studies.

Screenshots

Desktop (please complete the following information):
Safari and firefox