After tracking properly a page with button click, I am visualizing Unspecified value in the Dashboard Freeform. I double checked and the evar is properly populated and sent to AA. Do you have any suggestion?
Unspecified values in an evar report is an expected behavior because of its persistence. It depends which metric you are using in an evar report. Below is the document that will explain in detail about unspecified.
If you are using Visits, Unique Visitors et cetera then you would see Unspecified values.
However, if you are trying to check how many times that evar fired. I will suggest you to please use Instances metric. As instances will show you number of times the evar fired and will not show unspecified.