This problem has been happening (again) for some time (years). It appears (by
viewing the email headers) that (some) messages are still being assigned a spam
score, but it does not appear anything happens beyond that. A lot of spam
(even scored as "possible spam", etc., items are still being directed to the
main queues rather than the junk folder.
OTRS admins can set filters, which typically could divert any message with an
X-Spam-Score higher than X value to the junk filter, but X-Spam-Score does not
exist on our list of search options. We have X-Spam-Flag, X-Spam-Level and
X-Spam-Status - none of these are even in the email headers.