How to ensure that my issues are not moving to new Sprint while closing the old Sprint even though some of the issues are in "Ready for UAT". Also, I don't want to start two sprints in parallel because that way I wont be able to find the true velocity.

[Nic Brough -Adaptavist-]

Issues need to be "done" when you close the sprint, or they will move to the next one.  You can't have open issues in a closed sprint - that does not make sense.

[Harvinder Singh]

I agree with you what you are saying. But let me explain my situation first, the workflow is that the defects go for internal testing  from Ready for QA to In Testing and finally to Ready for UAT where client has to test the issues(stories mainly). 99% of the cases the stories are closed and defects are raised against the stories which can be further linked to the concerned story. So, 99% probability is that developers have not to work on the stories. The defects whatever are raised during UAT testing can be moved to new or upcoming sprint. So, if I don't close the sprint as there is a lag between the development and testing, I won't be able to get the actual velocity.

[Sten Sundelin]

What is the issue with just mapping "Ready for UAT" to the Done column, but without setting the resolution until UAT acceptance? Create new Stories/Defects/Bugs if UAT fails.

[Nic Brough -Adaptavist-]

Sten has covered what I'd do for that case.