PR4100 firmware update stuck at 99%

Saw this post and have had the same issue. But here is the fix YMMV this worked for me.
Current firmware in the drive is : 5.11.112 and would get the dreaded stuck at 99% Manual upgrade gave the message firmware file not found.

Rebooted the device and upgraded to this;

Then proceeded to upgrade manually to 5.25.124

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