I have always used 'Ctrl+Shift+Enter' > 'GTA V.exe' > 'End Process Tree' to quit the game. If I shutdown the normal in-game way the game freezes for a while & slows my PC down for a few minutes after even though the game has ended. Far simpler & easier to just kill it dead with Task Manager.
Obviously don't do that in the middle of saving etc but that's what I've done for the past ~3 years of playing & it has never once caused a problem so it's totally safe to do.
G