Since getting my Galaxy watch 6 classic last week, my watch hasn't been able to track my sleep. I also can't use the gestures and buttons features, whenever I try, it keeps telling me to put on my watch first, even though the watch is on my wrist. I've reset the watch and it still isn't working.
See what happens if your turn off wrist detection. Do you by any chance have a tattoo under the watch? I can't find the wrist detection on my watch 7, but it was there on the 4. Maybe due to all the complaints from people with tattoos, they removed wrist detection entirely. However, if you do have a tattoo under the watch, that could be the problem. Also, the watch must be snug.
Are any of the sensors working normally? You can try uninstalling and reinstalling the Wear app and Watch6 manager, then reconnecting the watch. If that fails, I would just return the watch as defective if you are still in your return period. If you are not in the return period, you are still in warranty, so you should put in an error report through the support tab of the members app.
