Strange experience booking this trip. Had started the search with Google Flights/ITA Matrix and found something for ~$790-800 per person, but could not get the booking to "take" from GF or via the ITA userscript.

Multi-city search on delta.com for SFO-TPE // HKG-SFO produced some broken fare at $3k-$4k per person.

I had to break it up into three pieces, SFO-SEA // SEA-TPE // HKG-SFO to replicate the $800 fare. But even then, I could not select flights. It would let me pick the first SFO-SEA flight, but when I picked a SEA-NRT-TPE itinerary it would give me the "oops" message and kick me back out to the starting page. This was if I was logged in.

In a private window and/or logged out, I was able to select the flights I wanted, and then login during the checkout process. Weird.