Itunes never stop updating podcasts
I had tried to address the problem through the settings.
You'll need to do one of the 3 solutions identified. My setting are set as suggested in your responses, and even when hitting "Refresh" manually after the auto feature is done does not download these back-episodes.
If you've waited at least 24 hours, login to Podcasts Connect with the Apple ID you used to submit your podcast, click on your podcast and click to refresh your feed. If your i Tunes listing still hasn't updated, there may be a different problem with your feed causing issues with i Tunes.
Libsyn has seen this to most commonly be the podcast cover art. But if the latest episode doesn't download, then you may need to fix common podcast RSS feed problems.
I get around that with a daily task that runs and downloads podcasts.
I believe I have posted this before, but I'll do it again for a refresher.