Erm, don't know how to say it more precisely, so I will describe, again, exactly what happen - I hope you will be able to draw conclusion, about which part fails.

So - after switching to hostmode, Your script start to cycle through speeds, in attempt to determine correct one. In case of my keyboard, it looks like this:

low speed -> it's enumerated properly, extkbd detects it, and for millisecond I'm able to use keyboard -> just (mentioned) milisecond after it, usbmode is killing it, to try another speed, so device becomes unusable again.

Then, process repeat, and usbmode reports failure, despite fact, that device was working OK (until it killed it by trying with new speed).

Conclusion - timeout before declaring "failure" at current speed, and trying next speed, should be extended by second or two.
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It's not only problem of low-speed devices - same happen for high-speed hub I was trying to connected, and, as reported, for some high-speed HDDs.
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If it still doesn't help, I may browse through script's code, and try to determine what I've extended, to make it work - but I was trying so many things re-hostmode (and it was more than a month ago), that I'm afraid I could give You wrong suggestions. I'm quite sure that - as author - You will know better, which value I've just described, by analyzing detailed description.
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If You have any idea how I could help (by other means), I'll be glad to do so. Just keep in mind that I'm still on kp51 (latest revision of 51 from repos), so I'm using corresponding usbmode.

/Estel