I may be misunderstanding how this works, but here’s the scenario.
Our community was finding that waaaayyyy too many old topics were being bumped with non-useful one line replies because the topics appeared in the Suggested Messages section at the bottom of all threads.
I changed the suggested topics max days old setting to be 14 days to try and reduce the effect:
This ways once a topic hasn’t had a reply in 60 days it can no longer be bumped save by user level 4 and staff. There is a handy theme component plugin to warn these members if bumping a closed topic.
I suspect that’s the sort of setting you may need to reboot the server, or restart the Discourse container, to get it to take effect? Have you tried that?
If it persists after container restart / server reboot then most likely a bug.