The submission on the Greek genocide committed by the Ottoman Empire in 1914-1922 that claimed 450k-750k lives [1,2] was placed ~34th on HN (7 votes in ~40 minutes). About ten minutes later it was gone, and couldn't be found among the first 300 submissions, despite the story not being flagged.
Since discussion of the 1921 Tulsa race riot that took place at the same time seems to have been allowed [3], I assumed this story was also within the rules. Is this not the case?
[1] https://news.ycombinator.com/item?id=24600458
[2] https://en.wikipedia.org/wiki/Greek_genocide
[3] https://news.ycombinator.com/item?id=22221180
I don't think this is shadowbanning. I have another definition of shadowbanning.
A post with a few flags get a small penalty, and with more flags it gets a [flagged] label and more penalty, and with even more flags it is autokilled. Perhaps the post got only a few flags? Perhaps you are overestimating the normal decay?
About the Tulsa riot, this site has a lot of users from USA (60%?), so it has a USA bias. [Hi from Argentina!] Post related to other countries sometimes get ignored.
Also, there is a bias for current events, and things related to current events. If tomorrow Turkey decides to bomb Athens, my guess is a repost would get more traction. (But I hope we can never test my hypothesis.)