I've been all over Florida, both by car and by sea. I used to be based in Miami when I was flying out of there in the late 80's. However I've had relatives on the west coast of Florida longer than that. I know the roads are flat, but as I said, I have trouble imagining that they don't continuously go up and down a few feet vertically for every 100 or so feet you travel horizontally.

The fact you had a consistent number prior and now don't seems to me to indicate it may have started working correctly after having some issues. However I will agree there could be something else up. A plugged up static port, a software change in what the developers decided should count as gain/loss or a bug that didn't get caught and the data from the sensor isn't tallied correctly.

The only reason I talk about gain/loss is that to me the elevation loss completes the picture. No it doesn't cancel out and go to zero. Both gain and loss are unique totals to themselves. Also, by using the gain/loss as a descriptor, I feel it make it very apparent that I am not talking about elevation. Elevation is simply how far above or below sea level something on land is.

edit... oh, I have had people think that elevation gain is just the difference between their starting elevation and the elevation of the place they stopped at. That's another reason I'm in the habit of using the term gain/loss.