I have had my watch for 4 months and the back panel came off yesterday. Like everyone else who has posted, mine has not been exposed to water. Is it actually worth following up with Samsung on this? We have had major issues with the company when purchasing appliances for our kitchen and their customer service is absolutely appalling considering how much of a loyal customer we have been over the years. Can the watch operate without the back panel?
I would contact Samsung and see what they can do if the watch is still under warranty , I'm sorry you're experiencing this , I suggest not to use it without the back before further damage occurs.
Sorry to hear that this happened to you I would recommend contacting one of Samsung Certified Repair Center at the links below to help get it fixed.