I've had my Fitbit Aria for several years, through several moves and changes to Internet Service Providers. I've never had a problem connecting it to wifi that was this difficult to solve, so I thought I should share what I discovered.
In February, I upgraded my Ubiquiti Unfi Security Gateway (router/firewall) to the latest version of the firmware (ver 4.4.44.5213844) and several peripheral devices dropped off my home wifi. What is more, a new SSID showed up with "_Iot" appended to my home SSID. So I now have two SSIDs (HomeSSID and HomeSSID_Iot) and interestingly, they share the same password. In troubleshooting my Epson printer I discovered that it could see HomeSSID_Iot (but not HomeSSID), so I connected to HomeSSID_Iot without altering the password and it started working again. I noticed the same thing with my Roomba when it started malfunctioning and coming on at all hours of the day and night. The same fix solved the problem. When I noticed my Aria was no longer connected to the wifi, I attempted to apply the same fix but neither HomeSSID nor HomeSSID_Iot showed up in the list of available wireless networks and the setup couldn't find either SSID when I typed them in manually.
The problem turned out to be caused by a new feature in the Unifi Security Gateway. In addition to creating a new SSID for 2G devices with the "_Iot" suffix, it now has an option to "Enable 2G Data Rate Control" that sets a minimum data rate that the network will allow for 2G devices to connect to it. The new feature is turned on by default with the new firmware and it sets the minimum bitrate to 6Mbps. When I disabled this new feature, the Aria setup immediately saw both HomeSSID and HomeSSID_Iot and easily connected to HomeSSID_Iot.
I offer this tip because other routers may be implementing similar bitrate limiting features.
Moderator edit: format
