Confusing RSS Issues

My RSS feed seems to be having some weird issues that just started recently (or so I have been told). Please note that I have not done any coding or site changing in several weeks.

The problem:
On my feed https://thetrinitymission.org/feed/dailyoffice/ everything looks fine to me. It shows a feed with the last 5 posts.

However, on iTunes, Apple Podcasts, and Downcast it only shows some of the posts. You can check it out by searching for “Audio Daily Office @ The Trinity Mission.”

I can post code if it would help. But conceptually, I can’t figure out why the feed page would correct but iTunes would be messed up.

Thanks,
-michael

The page I need help with: [log in to see the link]