Noticed a possible syncing problem: thread https://www.akiba-online.com/threads/graphis-complete-collection-2002-2016.1747701/ asserts in forum view that it has a new post by @yuifan128 (with an ID of 4237536) along with appropriate marking like the "NEW" button, yet after entering this thread the last post is from 2019 and it's not possible to mark it as read this way, Marking forum as read worked, but it's a workaround.
I deleted the post because it was just a thanks, (that solves what happened)
now it a case of it being removed from the alerts