Stryd has a barometer, but no GPS. The baseline elevation of your Stryd can be off due to variances in manufacturing of the barometer, and a few hundred feet is not unexpected. The relative elevation is very accurate (within 1 meter), more accurate than GPS (but it will always be off by the baseline level). We are considering adding a calibration feature to our software.
Contact firstname.lastname@example.org if you have additional questions.