For some recovery tips, turn off the watch now first, and then check the thread forums.garmin.com/.../1098983
Are you referring to the contents of \GARMIN\ACTIITY folder after connecting your watch to your computer? Are you missing all of the .fit files or just the last activity? If you've lost just the last activity and you have not yet synced your activities, then see what trux mentions regarding file recovery. Assuming you've been syncing with Garmin via Garmin Express or Garmin Connect Mobile so you actually have your data in the cloud on your Garmin Connect account, then it's not such a catastrophic event. Once you've synced to Garmin Connect/Express, then there is no critical reason to maintain the fit files on your watch, in fact it is not advised.
Yes, the activity folder has been emptied before the upload of the .fit file of my latest activity. All the .fit files in this folder are gone but the other activities are already in Garmin Connect so there is just one activity missing.
Thanks for answering.
I have checked the first 3 recovery programs for Mac since I have an Apple laptop, but it does not bring my .fit file back (only 2 of the 3 actually scan the Garmin).
And Garmin already wants to install an update on my watch. I don't do it yet, but it suggests that the one from last night did not go well, and not only for me. (I saved the activity folder on my computer before last update, but it had already been emptied at this point. That is so frustrating.)
Another good one for macOS: is DMDE
See post from Former Member - Accidentally discarded activity - vivoactive 3 Series - Health & Wellness - Garmin Forums
Thanks for the advice. It did not work for me. Probably the Garmin update erased everything. Crazy.