The completion rate is the amount of people who completed your form divided by the number of people who visited your form.
When accessing the FormAssembly form link directly (or if you are embedding your form with an iframe), accessing the form multiple times will count as one visit, as long as the respondent's cookie is present. In other words, if a respondent is using the same browser, and they have not deleted the cookie, even multiple form visits will only count once towards the completion rate.
If a respondent is accessing the form via the (REST) API publishing method then multiple visits count multiple times.
If you are using the HTML publishing method, then we are unable to track information for the completion rate.