About 3 days before you are past the AS JL block, then everything will show. This is not a caching issue. This is an AS blocking (hiding) award issue.

It looks like there is plenty of space so waiting 3 days is probably OK. If you want it before then read my workaround post:
How bad do you want to go and how many miles do you have?

That's fascinating. I was playing around with your trick and noticed that I could book flights on 2/22/2020, which is actually outside of JAL's window by a few hours. I wonder if I went ahead and booked it if it would error out or not.

Interesting tidbit and thank you for clarifying!

I would recommend not booking outside the window. I believe this is AS pre-caching the availability. While you can try it the one time I did space was not reserved (not surprising since it was outside the window) and my booking went into limbo with an error message. I think AS had it in a queue to contact JL to process it later but this requires manual intervention and if they have to do this too many times they might close down even this workaround. I ended up making a new booking once the window opened which actually did claim the space from inventory and issued a ticket, then I cancelled the limbo booking. But you can make a booking immediately at the booking window. I have had success entering booking details right before the window opened and purchasing immediately after the window opened.

Something is definitely a bit fishy on award availability using intra-Japan flights. Observe:

Oh, look, I can do HND-NGO-BKK with the long segment in J, short one in Y but who cares on that short a flight. Oh, wait, it errors out when I try to book it...
https://cimg1.ibsrv.net/gimg/www.fly...6aacb9ac08.png

So let's see availability on the HND-NGO segment I want, JL 201:

https://cimg2.ibsrv.net/gimg/www.fly...f18d954d8a.png

Ooops. I don't know if this is JL married segment availability or what, but clearly all is not right at the House of Chester...

No such message when booking on the JAL site. My guess is it is approved and the CrackerJack AS IT team will get around to removing the warning message by Christmas.

Definitely married segments but it should be bookable as such. What was the error? Did you attempt more than once?

Hi all,
I am wondering if anyone had tried changing JL tickets <24 hours before first flight.
i need to change my return flight now but someone(JL i presume? or AS...) seem to have taken control of my first leg - I havent done OLCI yet. any clue?

If by "taken control of my first leg" you mean you cannot change it online, this is standard AS IT failure. You should be able to do it before you have flown any segments but you will have to call in and if it is an Inter Asia only itinerary you may not be allowed to do it for fraud reasons but an itinerary touching North America should be no problem to change before departure of the first segment.

There is married segment availability. It shows on QF and CX and on those sites it is now showing J available (married) on both legs. I would call AS, tell them the website errored out and ask them to manually book it. Get them to try for J on both legs but if Y/J is all you can get take it. Ask them to waive the phone booking fee since it is a website error.

I too am getting ???phantom availability for JL award showing on AS. After an hour wait on hold basically got a sort of clueless agent who had no idea and wasn't willing to do anything to help......

Unable to book award flight - cant confirm space on partner airline
 

Does anyone know if there is a way around the error (or what the cause of the error is)
We're sorry, we aren't able to confirm space on these partner flights. Please try again and choose different flights, dates or cities.
when trying to book an award flight on JAL via Mileage Plan?

The flight is showing availability on AS search (and also on BA Avios search for reference) but Ive not been able to book it via AS for the last 3 days.