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After the latest iOS app update, my Flex hasn't synced at all. I've tried several resetting as suggested but still doesn't work. The battery is full, bluetooth signal is strong and no other bluetooth devices nearby. Please help.
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I already solved it by myself. It seems like the root cause was my phone's date&time set the function of "Set Automatically" as off. After turned it on, the problem is gone. Thanks for all your help anyway.
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Community Moderator Alumni are previous members of the Moderation Team, which ensures conversations are friendly, factual, and on-topic. Moderators are here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
Hello @CatarinaGift, thanks for joining us, it's great to have you on board! 
As you have already reset your Flex several times, my suggestion would be checking @HelenaFitbit's excellent tips and recommendations that have been proven very helpful for many members in the Community. However, if after trying these steps your tracker is still not syncing correctly, I would like to recommend setting your tracker up as a new device to reset the connection between the tracker and your phone. Don't worry, this won't remove any of the information stored in your account so far.
To set up your tracker as a new device:
- Open the Fitbit app and tap on the Account tab at the bottom of the screen, then tap on "Set up a New Device"
- Choose your tracker and follow the onscreen instructions to continue
- When the app asks you to replace your current tracker, please replace it and continue with the process.
I hope this can be helpful, give it a try and keep me posted in case you need anything else! 
Best AnswerI already solved it by myself. It seems like the root cause was my phone's date&time set the function of "Set Automatically" as off. After turned it on, the problem is gone. Thanks for all your help anyway.
Best Answer
Community Moderator Alumni are previous members of the Moderation Team, which ensures conversations are friendly, factual, and on-topic. Moderators are here to answer questions, escalate bugs, and make sure your voice is heard by the larger Fitbit team. Learn more
Hello @CatarinaGift, I hope you're having a great day.
Thanks for taking the time to reply and let me know your issue has now been solved. I'm very glad!
In case you have some spare time I would like to invite you to visit our Discussions board where you will find great tips and encouragement from other members and if there's anything else I can do for you, feel free to reply!
Happy stepping. 
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