Garmin Connect Performance Dashboard wrong format and not accurate

I created a dashboard for showing average speed over time for swimming activities, by day.  I only have one swimming workout per day.  The y-axis for the chart is "average speed (mph)".  When I check the values in the chart or table, they are not matching the values for average speed in the activity on the phone.  Also, a little annoying, the numeric format on the chart is in "time", e.g. 2:15 (with a colon), not a decimal number which is what mph should be and what is shown in the mobile app.