Hi Florian,
Thanks for sharing that link! I tested this out on my end, but I was not able to replicate the issue. I had my team do some testing as well, but the link was working for them too. However, I have seen a few other reports of this happening, so I would like to do some further testing with you to try to narrow down the source of the issue. Would you be able to first try testing for conflicts with your theme and other plugins by re-running the import with a default theme activated and all other plugins disabled? If you prefer to do this in a testing environment, the free WP Staging plugin will let you create a quick copy of your live site that you can use for testing.
Let me know what you find!
Thanks,
Jennifer