When running in the Mendix Cloud or your own server, make sure that the link/ path is proxied to your server. Unless your node is a sandbox, you can do this yourself in the node details. Click your node and open details, scroll down, select network tab. There you can add /link/ as request handler. Don't forget to toggle it to make it active
Allow guests should be set to false in order to let users signin before accessing content.
This looks like the same problem as in this forum post: https://forum.mendix.com/link/questions/85887
I have got her project package so I will try to look into this tonight to see if there is a config problem or it this is a bug in the current module.
Regards,
Ronald