A Microsoft file hosting and synchronization service.
I think I have found a work around. This is what worked for me on Mac and PC.
At the client delete the http shortcut in OneDrive online web interface by selecting the shared folder and then remove.
Now reshare the folder you want to share at the primary user. Not sure if you need this step (or the previous) but make sure you share with specific people and not anybody with the link.
At the client login to OneDrive online and go to shared. DO NOT click on "add this folder as a shortcut to My Files" to the right. Instead open the folder by clicking on it. Now click at the top click on "add shortcut to my files"
Although this seemed to work the day I posted, it seems like this is not a solution. Some of the buttons in the web interface have also changed since. In my testing since I have seen the shared folder sync correctly, but as far as I can tell it's totally random and mostly you will just get a redirect URL rather than a synced folder. In some cases, it will be correct for one family member and wrong at another and so it seems to be related to each user who "adds a shortcut to My Files". It seems the process of "adding" randomly adds a URL or Synced folder.