Just bought SR3 and I'm reading over and over that 2 dlc were disabled in order to avoid 2 gamebreaking bugs, my question is what specifically happens?
I'm not sure it was about any game-breaking bugs
-- as far as I've heard, it's those DLC themselves
which break the game by making the player character ridiculously overpowered from the very start. (I think one of them, for example, gives you vampiric powers, allowing you to bite people and drink their blood to regain health or something.) As other threads note, you can easily enable those DLC by editing an .ini file; it's just not recommended that you do so for your very first playthrough.