Hi Mahesh,
Before moving on, I would like to confirm more information with you for further research.
1. As for "Recently upgraded some email id to office 365", do you mean you have migrated some mailboxes to Office 365?
If not, please provide the detailed information about it.
2. Does this issue only occur to the forwarded emails?
3. What’s the type of the problematic attachment?
Thanks,
Jerry Cen