Cannot add members from my family group to new PC

Hi!  Thank you to everybody chiming in.  I may have a solution (similar to  andadm​'s solution)After chatting with MS support again and not getting a solution, I decided to install it the way I used to 5 years ago – via local accounts first and then logging in all family members one by one.  It was time-consuming, but it worked!  My laptop now has all my family members' accounts.  Here are the steps:

• Settings > Accounts > Other Users – click Add Account

• This will pop up:

Click “I don’t have this person’s sign-in information”

• This will then pop up:

Click “Add a user without a Microsoft account”

• The Create a user for this PC wizard will then pop up:

Proceed to create a local account for each of your family. 

Note: Before Microsoft Family existed, I remembered that this was how I made different local accounts for different users (re: my family) in my PC about 5 years ago (). So, it’s going back to old-school ways of doing things. 

• Log in to the account you created. Open Settings and in your Home page, there should be an option to sign in your family member’s MS account:

You should be able to sign in without a hitch. 

I know this is a bit of a roundabout way to handle this bug, but it is a solution that worked for me. It takes more work (the “allow sign-in” in Accounts > Family was such a time saver), but this will do for now while MS developers (hopefully) fix the bug.