For me it only crashed when I invited friends directly after the game, still seeing the win/loss screen. As long as I’m in the main menu, preparing for battle, or somewhere else but being in battle it works.
I hope that helps.
Same here but I’ve had this issues for around four years. I assume my account got flagged so that it I am blocked from adding friends. Or maybe since I indicated I am 18+ and from Canada, I cannot add anyone younger than 18 or from the United States. I managed to add two players from Brazilian these past few months, but that’s all. Instead of crashing my game, please just make a pop up message: "You can not add this person as a friend."