It could happen that the run or offline sync completed using the Android app fails to upload, and your data does not appear in the calendar. If this ever happens, please reach out to us at firstname.lastname@example.org so we can help diagnose the issue.
However, your data is not lost. As long as you don't delete the app, you may still be able to recover it.
Please navigate (in the Stryd Android app) to Settings -> Debug Options -> Files. Here, you can see the files from the Stryd app that are currently on your device. It will label the files as either recorded runs, or offline syncs. Keep in mind that the offline syncs may represent many runs. It just depends how often you perform offline syncs.
In order to attempt to re-upload one of these files, simply tap on the one you want to upload, and tap Re-Upload.
If you have any issues with this process, such as the runs still not appearing in the calendar or in PowerCenter, please reach out to us at email@example.com so we can get to the bottom of it.