Originally Posted by Zorak

Thanks, I understood your problem description already. When I said examples/screenshots might help, I meant of the search terms you are using @:-)

i.e. usually when something like this happens to me it's because I re-used a previous search and changed the cities to new ones and forgot that I'd restricted the settings or something like that.

Because if I just search HKG to LAX on Feb 12 one-way and leave everything else as the default:

Attachment 51528

¯\_(ツ)_/¯

But assuming there's nothing quirky in your search parameters, the only other thing that immediately comes to mind is that ITA searches for some period of time and then returns whatever results it has (which is not necessarily every possible available flight/routing) so if the backend engine is really really slow for some reason it might just be that it got as far as finding some nonstops and then gave up.