I am setting an evar on a page(say pageA) everytime on page load tag for that page. However, when i breakdown the pageName variable by that evar, i still see a large chunk of value for that evar as "Unspecified" for Occurrences metrics.
Also, say if i visited other pages and come back to that same page(pageA) where I am resetting that evar with the same value. Will this value be considered as a new value or because the value didn't change will it be considered as persistant value?
As per the design of conversion variable (evar) report there can be 2 cases when Unspecified appears:
I am assuming you are using out-of-the-box dimension 'Page' for pages report. If you apply 'eVar Instances' metric to your report, you will not get 'Unspecified' in the breakdown report.
Instances metric is useful when you want to see the number of times a dimension value was set without the hits where that value persisted.
Comparison of Occurrences and Instances can be found in the document: https://helpx.adobe.com/in/analytics/kb/comparing-instance-occurences.html
Now every time an eVar is fired in the server call, an Instance of the variable is increased. This is not considered as a persistent value.
Hope this is helpful!