In the recent past, I've successfully setup a few visualizations (line graphs) in Workspace with a weekly aggregation, but I'm struggling to get this to work now (while the data source is aggregated weekly, the visualization refuses to be anything other than daily).
To do so, I created a simple free-form table with the "Week" dimension and then chosen whatever metric I'm interested in (e.g., Visits, Conversion, etc.). From there, I create the visualization (right-click in the data table and choose Visualize). This previously gave me a visualization that aligned to whatever time-based aggregation I chose, but not anymore. If I wanted a daily grain in the visualization, I'd use the "Day" dimension in the data table.... Did something change in Workspace or have I simply lost my mind?
Interestingly, if I view the data table for any visualizations that I successfully created with a weekly grain in the past and then click the "gear" icon in the data table section, the corresponding visualization immediately changes from a weekly grain to a daily grain (example screens below).
Before:

Click the Gear on the Data Table:

Visualization now aggregated daily....
