Fwiw, another data point. I've been using graphene for over a year now and it has been super stable and reliable for me all along. When I first got a pixel to try it out it was very much experimental for me because I just assumed that all kinds of stuff wouldn't work. But after a week of use it was clear to me that it worked better in every way than my Samsung phone on regular Android and I made the full switch.
Where I live out in the country we have shit cell service so I rely on wifi calling and text. This was the primary thing I figured wouldn't work so well. But it turned out to work way better than my other phone.