If you are using a Coros watch, there are some circumstances that can cause your data to duplicate in the Stryd system. Often this is caused by a poor internet connection when the Coros app on your phone is uploading your run data after syncing with the watch. If the internet connection has issues, the Coros app may send the data multiple times, and some of these copies may end up on the Stryd servers. When that happens, you may have two runs in your account.
To avoid this problem, make sure you only sync your watch with the Coros app when you are on wifi. If you do end up with duplicated data, simply delete one of the copies either in PowerCenter or the Stryd app.