I don't have an Apple watch, but when Garmin/STRAVA aren't synching or I'm having trouble getting my activity uploaded, I plug my Garmin into a computer with the charging cable and search through the watch file folders for the GPX file associated with that activity. Once you're logged into the STRAVA website, click on "upload activity" and choose "file" from the upper left side.
You might only get partial distance from the file on your watch, but it's better than nothing. Conversely, you can just create a manual activity on STRAVA.
Hopefully this helps!
