I have set the user id to allow users to be tracked across visits. The result is that Returning visits percentage over time looks very correct. Before setting user id I had an issue where there would be almost exclusively new visits, which I know to be incorrect.
At the same time as Returning visits is working, the widgets “Visits by visit number” and “Visits by days since last visit” appear to be incorrect, the former showing that all users have 1 visit only, while the latter shows that all visits are within 0 days of previous visit. Both of these are confirmed to be incorrect, if the Visitor Log is consulted.
What could be the cause of this discrepancy?