What Causes a Favorite to sell out, when you never got notified quantity was getting low?

Hi HSN CS:

I’m so bummed out.    I’ve noticed several times now, most recently today, that items in my favorites list, just “sell out” and I never even got a notification the quantity was getting low.

The item was here yesterday, no notices on the item of low quantities, usually you’ll see something like, “20 left” or “18 left” even if it’s not one of your favorites.    But if it’s a favorite, shouludn’t I have received an alert?

Thanks,