Hi Rajesh,
Did you manage to fix this issue? I have the same issue on my Lenovo Yoga aura slim 7i. I agree that its unlikely to be a hardware issue. There are many reports online of people with the same issue.
https://www.reddit.com/r/Lenovo/comments/1j1cnmy/shift_keys_dont_work/
https://www.reddit.com/r/Lenovo/comments/1l2uvhg/anyone_else_having_issues_with_their_shift_keys/
https://www.reddit.com/r/Lenovo/comments/1j1x069/keyboardmouse_software_issue_yoga_slim_7i_aura/
I have followed every piece of troubleshooting I've found in the links above. Nothing has worked. As you'll read in the links, some people have sent their laptop to lenovo for repairs and even when the keyboard was replaced, the issue returned. I presume its a windows driver issue.
One thing I found interesting is what's seen in the first link. When I followed what they did - pressing both shift keys at the same time and then pressing C or X, I saw the same thing - it changed the volume or caps lock respectively. This demonstrates its definitely not a hardware issue with the keyboard.