When I first started playing GTA 5 online, there was hardly any lag at all.
Now I am experiencing 10 second lags at numerous times throughout the game.
I've also encountered the game lagging so much that it will not lock on to players when trying to shoot them and when it does lock on, shooting them does not take affect on their health because the game is so far behind that it doesn't realize I am shooting them.
Whatever has been done since the updates and expansion packs, it has made online play extremely frustrating. Fix the platform before adding more expansions. Its getting annoying!