I am not sure about the 3,3V anf 5V business.
If you have 3,3V Sensors, this might be a problem, if the Arduino tries to communicate with 5V with them, when they are not 5V tolerant (might destroy them).
Another thing: Do you have applied pull up resistors? Can be, that this is in some combinations running without, but normally with i2c pull ups are needed:
But careful with the 5V! I am not sure, but I guess, that the sensors might be killed by that.