Apple Health App, iCloud Backup and Restore

I was using iPhone 7 Plus for 4 years and 2 weeks back (on 17/Oct/2020) I purchased a new iPhone 11 with a trade-in option with Apple India online store.

I was syncing & backing up all my data on my old phone with iCloud (I had purchased additional storage in iCloud). I had my health data for the past 4 years on my old iPhone 7 Plus - It had logged all my activities, steps taken, walking distance and floors climbed amongst other data. This was great as it gave me weekly / monthly and yearly averages and it was an indicator for my workout routine.

As I had enabled iCloud sync and backup, I was at peace thinking that my data is safe in Apple Servers, till I used my new phone. 

After I unboxed my new iPhone 11, I used ‘Restore from iCloud backup’ option as that would save me from the hassle of installing and configuring all apps that I used in my old iPhone. Also, I wanted to ensure, all my data is restored in my new iPhone 11 so that I start fast with my new phone.

Restoration worked beautifully - all my apps installed automatically, with all configuration in place. So far it was good. I started checking each application and was happy that it was a smooth process.

Then came the shocker. I checked my health app and found my details (name, blood group, height, weight etc etc) in place but my activity data was missing. It had only one day data - that of 17/Oct/2020 - the day I switched over to my new iPhone. All my activity data was gone.

I was shocked and was at a loss. I raised a support ticket and a support executive helped to get lot of logs / debugging data but gave up saying, he (rather Apple) not able to retrieve my data.

What's the resolution to this issue? How do I get my data back?