Doctor said baby isn’t “thriving”

So it’s really disappointing that the doctor put this on my daughters check up. I got a bill for her routine shots so I called the insurance and they said that the doctor put a code that there is failure to thrive, not related to the charges on my bill though. I am really upset about it because she is developmentally where she is supposed to be, she is so happy and very active. She has only gained a few ounces since her 9 month check up. Went from 19lbs to 19lbs 4 ounces. She’s still at 50th % for her age. She looks healthy, she does not look underweight at all. It is just sad that the doctor says she’s failing to thrive. She’s in a stable household. It makes me feel like I’m the failure.......like I’m not doing something right and that’s why she isn’t thriving. She’s still nursing but I offer her food all day long. She eats sometimes and sometimes she doesn’t. It’s tough because I try so hard. I can’t force her to eat. It’s just really tough to hear that.