Go to this forum and follow the steps listed in the first post. After a recent FiveM update I started to experience this same issue of yours and I discovered FiveM was set to use my integrated graphics, which a while back I previously made sure they were using my GPU. However, it was changed, somehow, and after changing this to the GPU it hasn’t occurred again.
After following these steps go in game and set your graphics how you want them and they should stick on next relaunch.