IOS – Upgraded to iOS 9.0.1 and lost all health weight data

Yes - I see the same very small data sets from the 5s running iOS 8.

I also get over-estimates of my step count when running and walking yet somehow over the day, I believe the total counts are reliably the same small over-estimation of my actual effort.

My only conclusion is that the devices need to handle motion data from people with short legs, tall legs, stiff shoe soles, cushioned running soles, pavement and trail runs, etc...

I'm sure the engineers know that some class of people are over counted and another are under counted and my suspicion is that they are attempting to be as close to accurate for as large a group as possible and still work within the constraints on the firmware code size/complexity in the motion coprocessors and not drain the battery more than the allowed power budget for each device.

FWIW - the iPhone 6 is even better at estimating, still has lots of small data bursts logged to health app but still slightly over estimates my effort.

Looks like you need to encrypt your iPhone backups for your local backups to retain health data:

http://support.apple.com/kb/HT6357

Hope this helps?