I have the exact same problem. It started happening halfway through my canoe trip and aside from being really annoying, was also just disappointing not to get to log all that activity. I was able to get it to stop vibrating and cycling through the screens after Several attempts at restarting it but now it won't sync to my device and is four hours behind (the time around when it stopped working to when I was able to reset it). I talked with Fitbit Help, but they just cycled through all the stuff that's on the website before saying "well that's all I can do, you're out of the warranty period, here's a 25% of coupon but it doesn't apply to this, this, this and that. Thanks for reaching out."
It's super disappointing that they can't be bothered to do more or provide a full replacement product when it's clearly something on their end considering it's happening to a lot of users across a wide demographic at the same time.
