After setting ext:StopForumSpam to "enforce" on the beta cluster (T304111) [basically removing $wgSFSReportOnly so that it defaults to false per extension.json], channel:StopForumSpam seemed to stop working within beta-logs.wmcloud.org, pretty much at the same time:
We're still getting logs on the beta cluster (/srv/mw-log) for this channel, and they seem fine. In fact, the extension seemed to work fine in "enforce" mode according to the logs for that timeframe. It just broke them making it over to beta-logs for some reason, and then remained broken after I reverted the config change, since I didn't know what was going on. The only new logging change which should have been introduced is this block, since it comes after the reporty-only early return. But that seems pretty innocuous on its face to me, so I'm not sure how that would've caused this issue.