Hello,
We are experiencing a backlog of Moodle forums for 12+ hours. They look to be set on the Scheduler to be running every 15 minutes. That's that fastest we are able to run the cron without causing other issues. Did the scheduler change from 3.6 to 3.8? It looks like they are now queuing vs processing immediately. In 3.6 they ran immediately and until completion.
Thanks,
Barbara