Setup redirects to Login screen instead of final step when generating a new site package in step 3

Description

See Header. I've spent almost 2hrs debugging this now and am out of ideas - maybe someone else has one. Things I've tried:

• Comment out the logout line in the SetupController - no change. This line is not the reason for the logout.
• Comment out the line where the site package gets generated - this fixes the issue (ofc we don't get a site package generated and have to comment out the import method call for it to work) The logout seems to be caused by this single line, but I can't seem to figure out why. I also suspected it to be caused by an aspect or in a signal, but I couldn't find anything there. These two lines do not seem to cause it, as the issue persists even if the import method call is omitted - the package generation call is enough for the session to be discarded.

Steps to Reproduce

1. Create a new Neos project with composer create-project and run the setup
2. Proceed until step 3 (site import/creation)
3. Enter a package key and site name and press "Next"

Expected behavior

Redirection to the final setup step

Actual behavior

You will be redirected to the setup login instead of the final setup step. See video: https://youtu.be/JIuP8ZDBnl4

Affected Versions

Neos: All currently supported versions

Flow: n/a