Some Stryders have notice that RSS for their trail runs is lower than expected. For the RSS calculations, PowerCenter considers time spent in each power zone. If power during your trail run is the same as a comparable run on the road, RSS will be the same.
If your trail run has ups and downs, note that Stryd does adjust power while climbing or descending. Some Stryders have experienced that power hiking results in lower power numbers than running, and that it is challenging to maintain power running downhill. This might mean you are not in power zones you might expect.
Stryd does currently not accommodate for surface differences. If you are on sandy or rocky trails, your effort may be higher than Stryd is able to record.
If you have additional questions, contact firstname.lastname@example.org