To the author, your blog platform outputs an invalid canonical url for your content. It omits the `blog` subdomain which makes your canonical url point to a 404.
"https://assetnote.io/bug-bounty/2020/02/01/expanding-attack-...
Hm, perhaps the link has been updated by now? I am reading from Feedly on Android, and the link is the bad one I quoted. But from here on news.ycombi, if I click the link at the top, I get a valid link that begins with "blog."