I don’t have a Star so can’t say whether anyone has met this, but someone will come along and reveal all. In the meantime the two things I would suggest trying to get it to work is 1) unplug and plug in again the USB HD. And 2) restart the Star (not just into network sleep but into deep sleep or even power right off).
Best
If I understand correctly you suggest it did originally work until it went to standby and woke.
What make and how is it formatted? Some drives will potentially ‘go to sleep’ and that could be a reason it’s not seen immediately but you’d expect it to appear once it started up.
Did you try front or rear USB? Have you tried the other?
I assume this is a ‘portable’ size USB drive - most these days will run fine powered from a single USB port, some older ones might have had higher power requirements - a clue would have been a lead with 2 USB connections at the ‘computer’ end - one for power/data, the other for extra power.
I have a Nova and there is a setting which uses a bit more power in standby to act as a network server of attached USB media - if this is not on by default I’d consider enabling it to see if it gives more stability.
If your USB drive is set as a “music store” (i.e. was formatted by the Star, and you’ve been ripping to it from the Star), then it should show up under the “Servers” input now, not the USB input.
If you have a USB drive full of rips from elsewhere, and that drive hasn’t been “set up” in the manage music part of the app, as a music store, then it should navigate from the USB input part of the app.