So I'd originally had a thread on here which listed a bunch of tickets with one of my addons which the new site had inadvertently marked as spam.
Looks like me pasting more examples of ticket URLs also triggered the spam filter for the forums, and that got removed too.
I'll refrain from linking things this time around, but for the addon "Thousand Jabs", there were two tickets (IDs #12, #13) which existed before the site migration, I commented on those with some follow-up, and the tickets disappeared from the issues list. Navigating to the tickets manually showed that they'd been marked "Spam" as soon as I'd commented.
After looking at things further, I'd noticed that there were more tickets created after the site migration (IDs #16, #17, #18) which were all marked as Spam before I saw them.
As stated at the start, it also seems that putting a bunch of URLs in the body of one of these forum posts also triggers the spam filter... might want to wind things back a little bit?