MSPU writes this up as:
Microsoft Band 2 owners who are experiencing syncing issues with the mobile app on Windows Phones may feel Microsoft has abandoned them, but it seems the Seattle software giant does care after all. Microsoft has just pushed out an update to the Band app for Windows and Windows Phone, taking it to version 2.3.31002.0.
The update fixes a synchronization issue where users were receiving the cryptic: “System Error – There was an error. Please try again later.” error.
It also brings the usual bug fixes and performance improvements.
You can grab or update the Microsoft Band UWP app here in the Store.
See also my adventures hiking with the Microsoft Band 2 here.
(via WBI)