I have been working with XD for some years now and learned, that you can to save the file with a different name ("Save as..2) to the local file system (to have version history) and the shared link will stay unchanged. So, if I had created a prototype and shared the link with several people for review purposes, I can work on the file and save it with the difrent name, and just update the existing link to make the changes visible for the reviewers. If I wanted to create a new sharing link, the UI has provided "New link" option with me.
Since version 18.104.22.168 (or maybe a version earlier), XD has started to clear the shared link always when I save the file with a new name with the "Save as..." function (e.g. from "prototype_2020-03-16" to "prototype_2020-03-17"). If I saved the file with a new name, I must create a new sharing link, then send it to the reviewers and make sure they are commenting the correct prototype. The "New link" function is pretty useless if saving the file with a new name will do practically the same anyway.
Is this new functionaly a bug you are going to fix hopefully soon? Or is it an intentional feature to stay?