Hello @JPdebeer, welcome to our Community and thank you for your feedback. Despite many of the high end mobile devices are built with the same core specifications, not all are able to support the Fitbit app and the tracker's feature.
The difference with devices that are not listed is that we cannot guarantee it wont present issues or will work with all the features. However our teams are constantly testing devices to make wider the compatibility with nowadays mobile phones.
Since your tracker was working fine at the beginning it wont hurt to try the following suggestions mentioned on this post: Having trouble syncing? (here's how to fix this).
To see the latest list of supported devices, please go to http://www.fitbit.com/devices. If your device isn't listed, you can check the link at a later date to see if device support has been added.
See you around and let me know if you have more questions.
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