Hi Santhosh Sekar,
Base on my previous tests, upgrading of Tableau Server could show different problems a long the way.
However, those 'pitfalls' can be resolvable as long as the errors are shown or logged.
Post it here in the forum and the community will try to help you to solve it.
Please try to read the documents prepared by us that could help your upgrading:
There are precautions and preparation written on it before you proceed on upgrading.