Hi, I got the same issue now, while I'm writing.
Specs: Maximus VII Impact, updated to BIOS 2601 when it came out (beginning of april).
The message on the screen is:
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iROG3 is updating.
Do not shut down or reset the system to prevent system bootup failure.
15%% complete
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It started updating half an hour ago and it's still at 15% ... !!! It will probably take many hours to complete, and I hope it will start correctly.
I never got any problem until now. The only thing I could say is that the pc has been correctly shut down and unplugged (without power) for 3 days, it has never been unplugged before. Anyway, I start the pc and shut it down almost every day, but always witch power connected. Could it be the fault has been generated by lack of power? Or BIOS problem? Thank You!
EDIT: it took about 3 hours to complete the update. Than it booted up successfully, and now pc works fine. I noticed that BIOS lost its configurations, like fan optimizations and everything else. It seemed that BIOS was just updated. Another information is that I used the BIOS version 2401 for about one week, before it was withdrawn and the 2601 version was released and corrected.