My out-and-back yesterday resulted in a net elevation change of 10 ft, and that was most likely due to the fact I didn't start my watch until a few seconds into the ride.
I have the forerunner 910xt with a barometer. (No elevation correction.) I did notice that it was reading 80 feet higher than one of the signs at the top of one of the peaks, but that could have been just a high pressure system blowing in.
https://connect.garmin.com/modern/activity/1111162267
Have you looked up what the elevation change SHOULD have been for that ride using an actual map?