Multiple attempts to post this and get help - my tab groups randomly closed and they are all gone. I spent a lot of time gathering up tabs into the right groups for big projects and trips. Somehow a window closed - accidentally, leaving only my inbox one open. I tried to no avail to find tab groups, restore history (option not given), and other ways to restore this.

I had been excited about the option of tab groups, and in the past they always reopened after a restart. But today they disappeared in the middle of session. It's tons of work and time lost and I don't think I'll use them again. What a disappointment.