I ran into ghost availability on UA metal a couple months ago, trying to change dates on an award flight CMH-ITO.

Once I got excited for a moment when the agent said that she saw a routing (which hadn't showed up online) with saver availability CMH-EWR-SFO-ITO (or something like that). But then she quoted me the mileage cost as some crazy amount - and it wasn't a standard award price or two one-ways. I repeated it twice to make sure I heard her correctly. She insisted it was priced that way because I was "backtracking to EWR" and you're penalized for backtracking

I just finally gave up and left my itinerary as is. I'm really avoiding COdbaUA for awhile.