Can not longer access mybooklive/UI/#

With the UI gone, there’s no way to roll back the firmware since the UI is what handles firmware installations. Also, it appears there is no hard reset (ie. a mechanism to push the reset button for X number if seconds to force a hard or factory reset). Thus, your options are to return it to the store if it’s new enough or exchange it for a re-certified unit. I received my decertified unit and it works fine - just like new - but will never perform another firmware update.