The SIS has probably drawn conclusions from its investigations that could either clear or damn Yang. But it has been unwilling to even confirm any interest.
New Zealand's economy is already closely tied to China, our second-largest export market, and the future may well see this relationship develop further. But constant vigilance is needed to ensure New Zealand's independent foreign policy is not threatened.
As former Prime Minister Helen Clark noted: "New Zealand must engage with major powers in its region, but it should not be naive in its interactions with any of them." The silence on this affair seems indistinguishable from naivete.
Yang had not been entirely forthcoming over his past, having listed not the spy school he worked and studied at, but the intentionally vague "Luoyang University" when applying to become a resident in 1998 and then a citizen in 2004.
Aside from questions over what exactly the SIS has been investigating, the issue over Yang's provision of vague and apparently inaccurate references with New Zealand authorities also deserves more sunlight.
Just last month the High Court ruled a man who failed to declare criminal convictions when applying years earlier for residence should be stripped of citizenship. It should be noted citizenship is one of the few prerequisites to becoming an MP.
Ardern has inherited a role that includes oversight of New Zealand's intelligence agencies and will undoubtedly have been briefed on the Yang situation. She needs to reassure herself and then, in appropriate fashion, the public that the matter has been - or will promptly be - properly addressed.
Questions over New Zealand's independence, as well as the reputation of one of its MPs, are being asked. Neither deserves doubts to linger.