tab groups in secondary window lost on restart about 25% of the time.
I usually run with two windows open. Both windows have multiple tab groups defined. About 1 in every 4 browser restarts, all of the tab groups in the second window are gone. Completely. The tabs are all still there, but there are no groups anymore. They always survive every time in the primary window, I never have a problem losing them in that one. So this only seems to affect the second window if I have more than one window open.
I do not have any of the addons listed in the "this conflicts with" list from the README installed.