Occasional rides refuse to upload from my Karoo

I rode today, but the ride didn't auto-upload to the Hammerhead dashboard, or Strava.  The ride is still on my Karoo, but "upload" is greyed out and won't let me tap on it.  I've been unable to manually retrieve it through Hammerhead or Strava using my laptop.  Has anyone else experienced this, or does anyone have any tips?  Thanks, Craig