@Trey-10 I would check following -
1. Adobe Analytics and Power BI both should have same time zone settings.
2. Remove the date granularity fields from the data being loaded to PowerBI check the visitor count if that is correct?
3. When you include the date granularity fields the total values may show incorrect counts. The Adobe Analytics connector, default unique visitors field provide a sum for the date granularity selected, and while aggregating to higher levels it just adds up those values. In other words, it doesn't actually account for the number of true unique visitors.
I think, option is to use raw export that pulled the data from data warehouse and loaded onto a SQL DB. The raw data should have filed unique visitor identifier which can be used in PowerBI to do Count Distinct functions. That should provided accurate unique visitor numbers for whatever date granularity was selected. Lmk