I think it's normal for them to settle in to the weight they're meant to be at around that age. Mine was born at 9th, dropped down to 2nd, and then at 4 months was at 60th. She's stayed at 60th for 4 years now. It could just be she's settling into herself or just had a big growth spurt and gained in length instead. You say you do a mix of feeding. When she's bottle feeding, does she finish it every time or leave some? My daughter had a lot of weight gain issues at the start (pre-4 months) and when we were bottle feeding, I was told to make sure I was offering her enough that she was leaving some in the bottle at least half the time. If she's finishing every bottle, I would offer more per feed. Obviously, it's easier on the breast though because they just finish when they're finished, and you'll have a good idea if she's had all she wants.