Also contacted Microsoft/Xbox support (case 1501920117) 5 days ago. They were unable to resolve and it was escalated. I haven't heard of a resolution. I can log into Dungeons with the account used to purchase on Microsoft Stores, but I am unable to log into Dungeons with other members of the family group. Message I get is
"Game ownership not established"
"Sorry, you don't appear to own minecraft Dungeons on this account. Make sure that you are signed in to the correct Xbox Live account and restart the game"
Also contacted Microsoft/Xbox support (case 1501920117) 5 days ago. They were unable to resolve and it was escalated. I haven't heard of a resolution. I can log into Dungeons with the account used to purchase on Microsoft Stores, but I am unable to log into Dungeons with other members of the family group. Message I get is
"Game ownership not established"
"Sorry, you don't appear to own minecraft Dungeons on this account. Make sure that you are signed in to the correct Xbox Live account and restart the game"
Tried it on a family group account and seems to be working as well now.