if Strava is important to you go with a Garmin cycle specific device like the Edge 520 rather than a general purpose outdoor handheld GPS.
Strava does not recognise altitude data from all GPS devices, even those with an altimeter/barometer and might recalculate any elevation data. I swapped from an Oregon 600 to a edge 500 for this very reason.
My device has a barometric altimeter, why is Strava recalculating the elevation?
If you recorded your activity with a GPS device that has a barometric altimeter, but Strava isn’t using that data, it’s possible that device is not yet in our database or that the file you uploaded is missing a Device ID. We occasionally see this when activities get synced through 3rd parties so if you know the device is in our database, please try uploading the original file from the device. If you still have questions, please submit a support ticket and include a link to the Strava activity.
https://support.strava.com/hc/en-us/articles/216919447-Elevation-for-Your-Activity#whyrecalc