I had troubles with my Fitbit Flex activity tracker for about a month or more. I finally decided to communicate with them with through e-mail and address the issues. I did that last week and the answer was that they would send me a replacement. Good.
It's obvious that they can see that there's no pattern in my exercise and at time I lose recording my activities due to the problems the system has. The other issue was the exercise period confusion! I would go for a walk at 12:05 for about an hour and the system would show my walking at 10:00 AM! So it's now replaced and I set it up. I hope there will be no problem no more.
(Photo: The replacement device in its pack. It took less than a week to arrive. Thank to Fitbit for that but as you the charger USB adapter is included which I already had. I'd appreciated, Had they sent a wristband as I broke the large one and I know am using the small and is not very comfortable. I guess it's some $20 for a new one which I skip for now. There was no charge for the replacemnt)