Edit: this afternoon it's not syncing at all. It's not my error, I'm going to contact Fitbit because this is so frustrating. I'd switch back to my Blaze temporarily if I still had it. My iPad app always claims I don't have Bluetooth on, but my Fire and android phones recognize it.
The same was happening to me yesterday as I set mine up. I was switching from Blaze, so I was familiar with setup and never encountered any hiccups like this before. Then I keep getting random messages that Fitbit.com was down for maintenance. Sometimes Bluetooth or wifi disconnected, sometimes it worked.
It all seems to be working fine now, so perhaps Fitbit was having problems on their end. Keeping my fingers crossed that's it, because the disconnects and repeated unrecognition was maddening. I had no trouble switching my old Blaze to my mother and getting her all set up with it and a new account at the same time, so I'd guess the problem is specific to the Ionic.
