I don't think it's the cause.
I thought the issue was that the USB Port was disabled by the new WiiU update (it disconnects all USB Port not connected to a WiiU formated drive).
So, I thought that IOS58 had something special which wake up the drive.
But if you are launching the loader from USB, it means the drive is already powered and detected by HBC.
So it's not an IOS issue ...
Users started to test older version of the loader to find the first revision with the issue but had different results.
not everyone are reporting the same revision, and the reported revisions have nothing changed on the boot sequence