Write to hello@humannotai.net. A person reads it.
Some measures are read across years rather than weeks, and Daycurve will not estimate them from a short record. If your Health data does not go back far enough, the app says so and names how much it would need. It is not broken; it is declining to guess.
Daycurve only shows what your record can support. If a measure needs a category you have not granted, or readings you do not have, it says what is missing rather than filling the gap.
Check Settings → Privacy & Security → Health → Daycurve and confirm the categories are on. Apple's permission sheet grants one category at a time and a missed toggle is the usual cause.
The first read of a long record takes a while — there may be years of it. It happens once, and after that Daycurve reads only what is new.
On a new device, or after reinstalling, open Daycurve and use Restore Purchases. Purchases are tied to your Apple Account, not to the device.
Everything Daycurve holds is on your device. Deleting the app deletes all of it. Nothing is held anywhere else, because nothing is ever sent anywhere else — see Privacy.
Daycurve shows how it arrived at what it shows, and that is deliberate — if a figure looks wrong to you, the method behind it is on the screen. If it still looks wrong, please write, and say which screen and what you expected. That is the most useful bug report there is.