My problem is the opposite.
It's been like this for a while. I subscribe to a podcast and all I get is the first episode of that new podcast. I have to go to the iTunes store to download the others. Older podcasts, apparently before this bit of psychosis, download fine, but anything new, nope...
I don't know if there is an error log for iTunes. Perhaps it's having a problem swallowing the podcasts and isn't telling me?
iTunes has definitely gotten a little eccentric over the years...