Perfect app, terrible sync

I already rate this app once I downloaded it 4 stars, I was happy and satisfied for the functions offered.
Im using it for 2 months and now Im really disappointed about the sync function: its a weak and uncertain process that more than frequently corrupts or loses data.
I cannot understand the sync mechanism, I expect just the new data is transferred to the server but considering the increasing time the process takes, probably the app transfers all the data every time.
Me and my partner are using the app intensively and the sync function is a must. Unfortunately now is really difficult to change the app due to the by amount of data we already collected.

MarcoMilani about Feed Baby - Breastfeeding App, v2.3.5