Originally Posted by UA_Flyer

I would not be too concerned. There are no places you can connect to in Asia at the moment unless you have a second passport or permanent resident of a jurisdiction, which allows you to enter not as an American.

As noted, the SFO-HKG-SIN is currently in the schedule for purchase in the month of July until early August. Starting early August, you will see the flight is not available, but SFO-SIN direct flight is back on. Of course, anything can change based on demand and change of travel restrictions.