Interesting video here from YouTuber Josh Cahill, one of the bigger travel vlogger about being refused a 144hr visa at PEK in early January.
It's a bit of a rant and I think he incorrectly blames Air China - same would likely have happened if he'd flown Korean in.
Gleaning the details from video and comments.
Josh is a German passport holder.
Flying Air China ICN-PEK-IST with a 6/7 day planned transit in PEK.
Regular previous visitor to China.
Seemingly refused because on a previous visit he (or hotel) hadn't registered properly which makes him no longer eligible for the TWOV, and eventually returned to Seoul. (Josh claims this is a new rule, but I'd think in most countries any breach of previous visas would make you ineligible for TWOV/eVisa equivalents)
Of note at the time of posting the video here seems to be planning to book another ICN-PEK flight and use a 24-hr visa to catch existing flight to IST - i'm suspecting this may also be problematic