LPS

Thanks for the guidance. The issue on the sub-site was that WP-Cron was not running, so the site’s email queue never processed. Other sub-sites kept working because they had enough traffic to trigger their own WP-Cron runs. I added a server cron to run due events for all sites specifically, and notifications began sending immediately. No REST or database issues were involved. Posting this in case it helps someone else on Multisite.