I installed my 2nd gen unit over the weekend and it took me longer than anticipated to get the unit connected to the cloud. In the end this was "user error", but the cause was the UI on the prefix for the serial number. The dark theme in the app made the prefix dropdown hard to see and thus I kept trying with an "incorrect" serial number (moving my WLAN AP closer after each try thinking that was the cause since the signal was weak).
In short, the drop down is visually so different from the big numbers you enter that it doesn't look like part of the process. In addition to this, the prefix portion was really hard to even see on the screen. I would consider looking at changing the UI component type to make it visually more consistent with the numbers you need to enter and more obvious in general.
Hope this helps,