I've set up a connection between Power BI and Adobe Analytics, and I'm importing some data from a specific segment created for this study. The segment is created using Page URL, and it is at Hit level. One of the fields is the Visitor ID. However, some of these visitor ids show up as ::unique_exceeded:: or ::unspecified::, as you can see in the following image:

Is there any reason for getting this error, or is there a way to get rid of it?
Thanks!