This happens anytime I pause a ride. GC slowly climbs back up like you see in this image.....
There has been a problem with Garmin Connect for a few weeks. It is plotting the graphs using total time instead of moving time. When the Edge is paused no data is recorded. Garmin Connect fills in the data by ramping between the last data point recorded when the Edge paused and the first point when it resumed. When GC is working correctly that time period is not shown and the graph jumps between the two points in one second or so.