Some Podcasts are synced to app some are not

I use iTunes on Windows (11.1.4.62) to manage my podcast subscriptions. iTunes correctly downloads the podcasts and I can play them immediately from harddisk (not streaming).

However, when syncing to my iPhone only some podcasts (the ones I subscribed to years ago) are being copied to the iphone as a file for offline playing. Newer podcasts are being listed on the iPhone, but to play them I will have to make the iPhone Podcast app (2.0.1 (446)) download them again!

What do I have to do to make iTunes sync my unplayed podcasts as files for offline usage to my iPhone again?