Some Apple Health data canceled after switching to new iPhone

In the afternoon of the 30th of October I switched from my old iPhone 12 mini to the new iPhone 16. I have been using for more than 2 years the app Lifesum, which stores nutrition data to Apple Health. It's the only nutrition data app I have and it synchronizes only with Apple Health.

The Lifesum app has been correctly transferred to the new iPhone, too, together with all Apple Health values of the last 2+ years.

There was one big exception: the nutrition data, whose only data source is the Lifesum app, were actually completely deleted for all days before the 30th of October. This means that my Apple Health app lost the nutrition data both on the old and on the new iPhone.

Just one week before I exported some nutrition averages on a spreadsheet, so I am sure that all historical nutrition data were there before.

Lifesum on the new iPhone still contains all my data of the last 802 days, however they are not synchronized for the period before the switch of iPhone (mid-day of the 30th of October).

Can you please help me understand how that was possible and if I have any chance to recover the old data?a