just curious....were you wearing a footpod or any other garmin device?
No, I just wear my 235 watch and carry my iPhone in a Flipbelt. The watch seems to track very well on pace and distance.
a crazy thought....you have an iphone so i assume the Apple Health app as part of IOS and the phone is in your flipbelt. If you open that health app on the phone and go to "sources" and is there a option "Connect", and if so under that the option under "Allow connect to read data" is the "Steps" slider off?
Was thinking along the same lines, in that for some other "source" was recording the activity and feeding it into Garmin Connect, doubling the values. Same thing would happen if you recorded the same activity on two garmin devices that were linked to the same account.
Hmmm, that may just be it!