thanks for all posters, i have the same issue in some of my websites
i guess this happens by the Akismet to increase site security, because spammers look for posts that have high page authority and try to comment on with anchor like to get back link to their sites.
and it’s known in some big forums and in social media sites that any post should get engagement form users in the first 30 day from the article has posted, and then comments closed in that topic.
