Yeah, sometimes you have to do that. But sometimes unchecking the box and manually setting the elevation offset will work, and sometimes you can scan through the Altitude column in the "Edit" view to see if there are one or two anomalous values and just fix them directly. If there are a whole bunch of bad values, yeah, you might have to clear the entire altitude column.

I wonder whether part of this could be a mismatch between metric and imperial measurements. Rockdude mentioned he rides at 6000 feet, but that Aerolab screenshot looks like the distance is in km and the elevation is in meters.