Had issues creating a new tab group in Safari - I'd create it, and then Safari would seemingly resynch things to a state where the group didn't exist. Eventually I quit and restarted Safari just to find all of the "Untitled" tab groups I had just tried to create. And of course the other tab groups were not synchronized to what I had open when quitting. God damn it, this would be a great feature if it actually worked like a human would expect it would work.