When the batteries are removed from the scale, the default date and time (01/01/2000) are restored as soon as new batteries are installed.
Be sure to perform a connected measurement after each battery removal / replacement to update the date and time.
If you have not done so, your measurements may have been synchronized to a previous date / time.
*credit to Sylvain of iHealth Labs EU
https://helpcenter.ihealthlabs.eu/hc/en-gb/articles/360000008049-iHealth-Lite-HS4S-Wrong-date-and-time-of-Offline-measurements