My older activity is missing
What you are seeing: Today's steps are fine, but you cannot see last week's or last month's steps. Your history starts abruptly on the day you set things up, and older days show nothing.
Also covers: why can I not see my past steps, my step history is empty, my old activity did not transfer, previous months are missing.
What is happening
There are two separate reasons, and neither is a fault in your setup.
1. Source apps sync forwards, not backwards
Most source apps behave this way. Fitbit and Garmin generally share a limited recent window when first connected, but not your full history.
2. Health Connect limits how far back apps can read
Health Connect deliberately restricts how much historic data an app may read without additional permission. Even where older data exists in the store, some of it is out of reach by design.
What you can do
Wait. In most cases this resolves itself: your history builds forward from the day you connected, and after a week it looks normal.
Check the source app has data at all. Open Samsung Health, Fitbit or whichever you use, and confirm it shows the days you are expecting. If it does not, the data was never recorded and nothing can recover it.
Do not disconnect and reconnect. It does not trigger a backfill, and on some apps it resets the sharing start date — which makes things worse rather than better.
On iPhone
Apple Health keeps your history on the device, so once you allow access it is generally available rather than starting from today.
If your iPhone history looks truncated, check that all three types are turned on: Health → profile picture → Apps and Services → The Ismaili. Turning on a type you had previously left off makes its history readable.
Challenges and missing history
A challenge counts the steps recorded during the challenge period, so history from before you joined would not have counted anyway. If a challenge total looks wrong for days you were definitely active, see something is wrong with a challenge.