IAR IDE v7.80.4 rebuild modifies the hex file already generated

I'm working on IAR IDEv7.80.4. Its been a while I used this IDE as the project is in maintanence state, and only needed to do bug fixes when it comes. Recently I just opened it and built my already released code (whose hex file is already tagged) and then I compared the hex generated. And unfortunately, there is a difference , a strange behaviour.
I rechecked by using a previous code revision and still there is difference in the hex file generated after build and hex file before build.

Please let me know the reason why this strange behavior occurs, or let me know if you have any questions on my observations.
Thanks in advance