There is a similar problem on AA.com, again with MNL as the destination and using JAL from NRT-MNL. AA uses the excuse of "the fare is no longer available on JAL" just like UA saying "the fare is no longer available on ANA".

Call me suspicious, but it seems a little coincidental. I wonder, and it is only speculation, if UA and AA want to publish fares that are competitive with the asian airlines and Delta but buy very limited inventory on the NRT-MNL segment. Thus the fare is "sold out" fast but UA and AA don't update to the new higher fare.

No matter what, it is annoying to see a fare that is not available once to say nothing of seeing the same unavailable fare for days on end even though it is still not available.