Someone updated the title.
It was originally "'flightsearch - miles. NotAvailable? partners" which I agree is unclear which is why it took a round of back-and-forth to understand what the actual issue was.
Now someone (presumably a mod) added "Online issue? App seems OK" in an attempt to clarify that this is a bug, but I agree was still extremely confusing what was being asked.

To answer the question posed by OP:
The "Not available" under Flight Details is not an actual reflection of the flight not being available. If there was zero availability, the flights wouldn't show up in search results.