The "incomplete day" indication you're seeing on your retention report graph is a normal feature of Mixpanel's Retention report. This is explained in the Retention: Measure engagement over time documentation.
Specifically, the documentation states:
"Boxes with an asterisk (*) indicate that the data is still in flux and not set yet because the time is still ongoing. Hover over a box to see when the last qualifying date for that bucket will occur."
This means that for the most recent time periods in your retention analysis, the data is not yet complete because users still have time to perform the retention action. Mixpanel marks these recent, incomplete time periods with an asterisk to indicate that the data may change as more time passes and more users potentially perform the retention action.
This feature ensures that you're aware of which data points are final and which ones are still accumulating data, helping you make more accurate interpretations of your retention metrics.
