Hi there @SuryaGopal!
Don here from Shopify.
Our developers are aware of and investigating an issue affecting the addition of featured blog images by users other than the account owner.
This is being looked into and worked on now, but in order to track how you've been affected and ensure you get an update, I'm going to send out an email to the address we have on file for you here shortly so I can escalate this to our tech team.
If you can just reply to the email I send out to you shortly, I will be able to escalate this and proceed.
All the best!