podcast wanting to re-download

Hello!

I have a small but weird issue that's really grinding my gears.

Occasionally when I open iTunes, podcasts that I have already downloaded will show the cloud symbol next to them and need to be downloaded again.

Has anyone seen this behaviour before?

It's not the end of the world except I backup my local iTunes library to a NAS and then point my Sonos at it so my backup is constantly removing the tracks and reading them once I have re-downloaded them.

Thanks in advance for any thoughts or suggestions!