Can't speak for GP, but in the 5-6 months or so I've been using it, most of my issues have been with keyboard navigation breaking or not working in some of the apps. It's gotten better with regular updates though and has been pretty solid. Other stability issues seem to have been deeper as since switching to a mainline kernel install (6.16.x) I haven't noticed any deep issues.

Pop has kept kernel updates well ahead of Ubuntu though, I just switched sooner than they seem to have.

it doesn't seem to handle multiple monitors very gracefully yet, at least when I used it & on my setup. Felt a little bit slower than gnome and less stable across the board.

For example, the top-bar UI doesn't render certain app icons properly, which was driving me crazy. Maybe it's a settings/config thing. My opinion is if cosmic isn't a drop-in replacement for gnome with extra bells and whistles, im not going to use it.

For all I know, it could be a lot better than gnome at this point. But for a daily driver that I'm working in, I need the stability of gnome over the 'cool factor' of cosmic.

I really liked the direction it is heading and will be using it eventually. Worth installing and trying out!