Recently I moved from the U.S. to Canada as a result of which (arriving in Quebec in January) I have not been on my bike or even looked at Garmin Connect....yesterday I rode for the first time and when I synced found 11 rides that I never made. 10 of those are in Guadeloupe!??? One is in my neighborhood but on a date when I was in the U.S., before we moved. Has anyone seen this before? Another odd thing, which may just be related to a software update on my 810, but I found it odd to get a "Welcome to Garmin Connect" email when I've been using the site for some five or six years... Certainly I can go and delete the random rides, but I would like to understand how someone else's activities are ending up on my account and if my personal information is thus exposed to them.
So I have been looking at little more closely at Garmin Connect and what I found is a second 810 with a serial number different from mine. i'm guessing, whoever owns this one must be frustrated that none of his/her activities are showing up on their Garmin Connect. I have since deleted this second Garmin 810 from my account and deleted the 11 activities from my Garmin Connect account. We'll see what happens now...still think it's weird that someone's device would suddenly show up on my account.
You should really report this to Garmin support so that they can investigate as they may well not be aware of it - they do not review the postings on here systematically so won't pick up this Forum post