It was [dead] but not [flagged] [dead], which means it was killed by automatic filter. We can only speculate on what that filter might be.

Probably anti-ban evasion signal (user was previously banned, created a new account, gets shadowbanned on spot)

I agree that shadowbans are an underhanded measure that doesn't belong in a site like HN. I always vouch [dead] comments made in good faith

I've seen several strangely dead comments today, perhaps the automated filter has been updated and has some gremlins?