I too, was experiencing great frustration because tab groups that I created on the Mac air, with times not appear on the iPad or iPhone. Tab groups are an absolutely wonderful feature. So after many unsuccessful searches, I spent some time poking around. The steps I was taking to attempt to open the tab group were what seems intuitive enough, that is, open safari, touch the bookmark icon at bottom, click on tab group favorites and poof I thought I lost them all. Instead try opening safari and touching recent tabs icon in lower right, then touch what I have recently heard described as the burger icon (three horz lines). This is where I found my tab groups intact. Not sure if it suppose to work that way or not. But for my situation I found what I thought I had lost.