Hey @Matildesolsvik, 
Thanks for your post and sorry for the delay. Please note that if you did not have sufficient reception during the time of saving the activity, that may cause issues with syncing once saved.

As a first step, can you please force quit both the Strava watch app and the app on your mobile device?
To force quit the Strava app on your watch, press and hold the side button until the shutdown screen appears, and then press and hold the digital crown until the app closes. You must be in the app to force it to close.
 Please follow these steps:

1. Log out of the Strava mobile app on your iPhone.


2. Use the Watch app located on your iPhone to force an uninstall of the Strava Watch app. Note that it may take some time for the app to be fully uninstalled from the Watch face.


3. Confirm the app has been uninstalled from the Watch.


4. Uninstall the Strava app from your iPhone. *Please make sure not to delete your Health data as we now only sync the last 30 days to the Health app


5. Force close all apps on the iPhone.


6. Restart the Watch and iPhone.


7. Download and install the Strava app on the iPhone.


8. Confirm you are logged into the Strava app.


9. Confirm the Strava app has been installed on the Apple Watch.


10. Unlock the display on the iPhone and load the Strava Apple Watch app.


11. Watch for and approve prompts on both devices.

If this doesn't resolve the issue you are experiencing, please submit a support ticket and someone from our Support Team will be able to provide additional troubleshooting steps.