I followed every single word and step as described in the sticky update post.
I've got a install failure while updating to 2.8 (helix rack, with controller turned off). Also the updated stopped, for an error.
Reboot in boot mode and tried again, the install does stop at 5% and fail again.
Tried rolling back to 2.7 or an earlier firmware in boot mode, keep failing at 5%.
Please help, this is a fresh unit with 3 days of life....
I encountered a similar (perhaps the same) issue during beta testing. The update stopped midway, as I was expecting, and then stalled. Helix Rack would not reboot, and the Updater program would no longer recognize it when connected (i.e. it was not 'enumerating' in Line 6 Updater). Here's the advice I received from Line 6 at that time, and it worked for me:
.... if it is not enumerating in Line 6 Updater you may want to try to put it into manual update mode and see if it enumerates.