Strava does a lot to “correct” the data that gets sent to it. Sometimes this means it gets it wrong, particularly with elevation gain. That ride is one that always goes wrong. There’s not anything we can do to correct this at the moment, we know the data that gets sent is correct.
We are currently working with Strava to solve this problem. We expect it to be fixed by the beginning of July 2018
Update. This issue is now resolved. Make sure you have at least version 2.7.0 of FulGaz