Yes.
It’s known as phantom availability and IME is most common with CX and JL, but can happen with other carriers.
If the sector shows availability of QFF, check BAEC or JLMB.
If it’s also showing as available there, push the QF agent to search again. If they still can’t find it, HUCA.
So the flight that they couldn't see yesterday they can now after I called today. However, the consultant I talked to over text before I called still couldn't see it.
With both consultants I asked (1 on phone, 1 on text), neither were able to see this booking (which I was only able to see just this morning):
This also doesn't seem to appear when you search on the British Airways website. I'm guessing this is another case of 'phantom' availability?