UPDATE – April 23, 2021 – 5PM Eastern
Apple is reporting that most shows that disappeared entirely from the Apple Podcasts directory should be live in their directory now. If your show is still missing please contact Apple Podcasts support via: https://podcastsconnect.apple.com/contactus
Starting yesterday, April 21st we began to see reports from podcasters that there shows were missing from the Apple Podcasts directory. We reported this issue to Apple and they escalated it to their engineering team. They are actively working on fixing the issue but there is no ETA at this time.