Analytics and Visitor ID Service is implemented using DTM. We uses AppMeasurement 1.5.1 and Visitor ID Service 1.5.2. The site uses custom tracking servers/CNAMES like stats.sitexyz and sstat.site.xyz, and we have set the Analytics Tracking Server fields as well as the Marketing Cloud Server fields to the same as the CNAME record.
However, not all browsers (who accepts 3rd party cookies) do get the demdex.net cookie set, why we won't have same visitor ID across different domains. That is a major issue for us, as we need to do cross-domain analysis with data extracted via data feed or Data Warehouse.
Have anyone experienced same issue, and have an idea of what is going wrong here? Any feedback are appreciated.