My gps was stuffing up too as it kept stopping losing locations . I had to use Simon’s hill climb as we ran next to me and then use a contour map to actually check how much it really was.
The quicker I turned around at the bottom, the lower down the hill the GPS said I went. If I rested a bit at the bottom, I got less climb for the next rep
Bruce gave me some data and looks like I actually did over 650m, strava is very wrong.
I quite often see an anomaly in GPS data, but yesterday, my Watch, Garmin Connect, and Strava all said the same