I had tried West Coast TO Asia as you had written in your original post.

Now, I tried TPE/SEA and the site behaves in the same manner as the one you describe.

I tried HKG instead of TPE and it works on some dates in September, both in J and in W. J is quite expensive (510,000 miles), W is more reasonable at 175,000 miles.

So you may have to show some flexibility in the choice of city pairs.