Pay attention to the date and time of the balance
If you removed the batteries from the scale and made offline measurements, your measurements were probably synchronized to the default date and time that the scale recovers after reinserting the batteries (ex: 01/01/2019 at 01:00).
Reconnect the scale to the application to set up the correct date and time.
Multiple users have the same weight?
If several users registered on the scale have a similar weight (at +/- 3kg), only the first of these users will be able to take offline measurements and synchronize them later.
If multiple users have a similar weight (at +/- 3kg), make online measurements only.
*credit to Sylvain of iHealth Labs EU