Hi mama! At 24-25 weeks, babies are usually weighing around 1.5 to 1.7 pounds (roughly 680-770g), so the 600-660g range your app is showing sounds a bit on the lower side, but honestly every baby is different, some mums I know had babies measuring lighter at these scans and caught up beautifully by the next one. The thing is, ultrasound estimates can have a margin of error too, so if your doctor or specialist isn't concerned about the growth curve, that's what really matters. I'd say just check in with your own gynae or scan clinic about where your little one is plotting on the growth chart, they'll know best if there's anything to monitor or if baby's just tracking slightly lighter than average, which is totally normal!
I would say best not to follow the weight stated in this app. You can only use it for reference. Just follow your gynae. If your gynae did not mention about eating lesser or more for baby weight, it means your baby is growing well.