To fully understand the Elevation Gain/Loss metric displayed during your activities, it's first necessary to explain the different areas where this data is displayed and how to interpret the different fields.
Certain activities such as hiking and trail running will, by default, have a data screen that displays the elevation gain/loss as a metric tracked throughout your activity.
However, you can also customize data fields to display this metric from within the COROS app. To see what data fields are displayed for any workout type, select "Workout Data" from your device homepage.
Next, select any workout type from the list which will bring up the current data fields to be shown during your workout. From here you can select any of the "Pages" which will give you the option to change/customize the fields as you desire.
When scrolling between Pages during an activity, the "Elev Gain" data field as seen below is displaying the vertical distance ascended, as measured by the GPS and barometer of your watch.
However, if you are navigating a route downloaded to your watch, there will be an additional data screen (below) that displays the elevation gain/loss as measured on the downloaded route. There may be times where the downloaded route and recorded data from your watch display different elevation gain/loss measurements.
There are numerous factors that may lead to a discrepancy in the two data fields, such as slight differences in the route you've taken compared to the route taken by the individual who created the route downloaded to your watch.
Rest assured that this is not uncommon to see, as the process of recording a route (no matter the platform) is dependent upon the accuracy of the device used to record the route. It is also important to keep in mind that +/- 10m on elevation measurements are considered accurate for any GPS watch.