If you see a duplicate Activity in the Feed on your Android device, don't delete it!
Just log out and back into your account within the Strava app, and everything should appear normal. This is a small glitch that sometimes makes it seem like a ride, run or walk has been duplicated - but if you delete one of the 'duplicated' Activities you'll actually delete both, which will cause you to see the Missing Resource error message.
If it's too late and you've already deleted the Activity, have no fear - we can get it back for you. Just create a new support ticket on the Strava Support site providing us with as much information as possible about the Activity and when it was deleted.