Yesterday, August 27th, normal spam filters were down.
I had compiled spam assassin’s system-wide rules to speed up processing. Not all of the rules can be compiled. An automatic sa-update that updates the rules created a situation where non-compiled rules conflicted with compiled and spamassassin aborted.
I changed the cron job that runs sa-update to re-run sa-compile afterwards if there are any rule changes. Last night an automatic update changed rules and sa-compile ran automatically and everything worked as intended.