Some of the weight loss may be due to swelling and the obvious removal of the abdominal pannus with the tummy tuck.
I'm I losing too much weight after BBL/TT?
It depends on why you are losing the weight. During the surgery excess skin and fat was removed as part of the tummy tuck. This obviously weighed something. The weight gain after surgery from 171 to 178 was likely water weight gain. Was all the fat that was liposuctioned put back in? If it was not, then that could account for some weight too. Are you eating like you were prior to the surgery? If you continue to lose weight then yes it can affect your results as weight loss does lead to decrease in size of the areas where fat transfer was done.