The most-recent example concerned someone who was giving-away his music. But, nonetheless, “it happened again.” A thread that had received no activity in more than 3 years suddenly re-appeared on the list of “latest posts.”
This happens several times a day …
Just look at, say, “Off-Topic Chat.” “Math and Physics for Creating Games” is supposed to have seen latest activity "9h" ago, but it actually hasn’t seen a single post (mine …) since November.
I’m going to start listing them as I find them. Here’s one from September, 2016. Someone replied to it, which means that “it showed up again.”
It these message are spam, please flag them as such. Please don’t list them here.
I saw one that was replied to that was 12 years old, LOL.
Another: 'Remembering the Fallen'
The problem, Bart, is that they’re not “spam.” They’re legitimate topics, but from months or even years before. They appear on the list when they have had no activity whatsoever, but, there they are [again]. (The list should only include topics that are recently posted or recently replied-to, but sometimes the list includes seemingly-randomly-software-selected topics that are neither.)
Maybe if we start listing them, the site owners and/or the company that owns Discourse will (a) recognize that a problem with the software actually exists, and then (b) find a pattern, find the bug and fix it.
I think it would be inappropriate to “spam” either the original topic or the very-recent reply if there is one. (Often: there is no “recent reply,” but, “there it is [again].”)
In the Vbulletin iteration of this site run by CGcookie, the code included an auto-locking mechanism which closed topics after not seeing any new posts for a year.
However, the site now not only does not have such a mechanism, but the suggested topics feature frequently shows very old threads (which encourages the issue being described here).
The way to fix that would to have the suggested topics feature biased toward recent threads and combine that with a new auto-locker.
The issue is that a thread can be bumped by a spambot. The system (or the moderation team) can remove the offending spam post, but the thread itself remains bumped. This makes it more likely for someone, not paying attention to the age of the post, to post a response.
All the Discourse “hops”, and spam still gets thru?
Not as much as otherwise. These days, the system handles quite a few of those issues immediately. We typically only have to deal with really clever spambots or real people paid to spam for others.
Still, whether handled by the system or by moderators, it seems those threads still get bumped and “unbumping” them doesn’t appear to be particularly easy.
Smart bot… It would make a nice browser extension, join another Discourse forum, get the tutorial and other nags done automatically.
Fweeb – (“bless you, my son … I have done what you have done and then I gave up … but … bless you, my son” …) all things considered, I would adopt and then implement a rather simple blanket rule: “if the topic has been inactive more than 90 days, it becomes permanently locked.” … … Forever.
If any human being(!) seriously wants to revisit the topic, they know what to do … it’s called a hyperlink.
Whereas “bots,” trolling algorithmically as they do through “the URL-space” of a particular web site, will simply discover that most of the links don’t work anymore. (And, they will never know.)
'But also, fweeb … yes," I fully appreciate what you and your team do for us every day … having briefly done so myself (for a much, much smaller site) before throwing my hands up in disgust. And so, I thank you all … 
… @>-±– … “here’s a rose …” … for not throwing up your hands. “Yes, we see it. Yes, we thank you.”
“Yes, I’m/We’re just trying to help.”