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Hi, khurram. Welcome to the Backdrop forum!

That's an unusual problem that hasn't been reported before. Can you provide more information? Did the upgrade happen without errors or warnings? Can you check the Backdrop "Recent log messages" under "Reports"? Are you using any contrib module related to users and passwords? (You can copy/paste the list of contrib modules by going to Reports > Debug information).

I had a similar problem with an D7 site I was upgrading to Backdrop, but mine related to inability to log in (to the D7 site) on my local lando dev site. I could log in on the public site but not on the dev site. It turned out to be an issue with the ssl setup. 

Khurrum - is your problem just on a public site and not differences between a dev and a public site?

OK i will try with a fresh install of Drupal up-gradation to Backdrop without any contributed module.

Thanks for responding!