UdayKumar Hi,
I can only suggest to post a sample example of the two cases with all relevant settings visible as best as possible in order for someone who is used to deal with 3D models, materials & shadows could help you. Add the exact beta version, or RC1, of Godot you are using.
Do not hesitate to also try another release, for instance a sample basic scene which shows the issue, on 3.5.
Also checking github issues may shows a currently open issue related to your case.
By the way, does the material settings you are using are correct ? Some materials may not working with shadows and/or are not able to process shadows they should deal with for some reason (shader issue for instance).