Stability issues. That's really from the engine or similar, not the scripts. Starfield did well here. Fallout: New Vegas tended to have problems that accumulated for me over the course of a given game.
Performance issues. Fallout: New Vegas and Fallout 4 both took increasingly longer to load the further into the game one was. I don't recall Fallout 76 or Starfield doing this. Up until Starfield, the 3D games had various situations where one could see graphical artifacts.
Scripting issues, weird interactions between quests, etc. That's been a problem for the whole Fallout series, including the isometric games -- lots of scripts that can interact in weird ways. I even managed to break one Starfield mission last time I played, though fortunately could recover by restoring an earlier save, and that's been pretty solid.