Thank you to everyone who contributed to this very informative thread! I've read a lot of it and believe my itinerary qualifies for TWOV but would like to double check with the experts here:

Aug 13 LAX-PEK (arrives on Aug 14)
- layover at PEK for two hours, presumably staying airside and not entering into Beijing but don't know how passport control works for connections at PEK
Aug 14 PEK-HKG

Aug 16 HKG-PEK
- entering into Beijing, can I use 144-hour TWOV being in transit from Hong Kong to USA?
Aug 21 PEK-LAX

The flight HKG-PEK is on Hong Kong Airlines, so are there any specific concerns with them allowing boarding for TWOV?

Thanks!