I should note that the Rossini 2.1 update is a full control board update to the Rossini unit, not simply an app update or network board firmware update. This is much more like updating the BIOS for a PC, then reinstalling Windows whilst also updating every single driver.
The vast majority of issues which I have seen with updates are rectified by a hard power cycle of the unit before starting the update process, and the rest tend to come down to local network issues which for one reason or another prevent the unit from properly communicating with the update server to download the update (resulting in error messages). As @Anupc suggests, firewalls and VPNs are potential causes to temporarily bypass if issues do arise. Simplifying the network chain in cases where issues are experienced is a very good place to start.
With all that being said, these comments have definitely not gone unheard. We are going through and thoroughly stress testing the update procedure on the back of these comments to see if we can improve the process to provide a smoother experience in future.