I started listening to a podcast called 'The Besties', it's a Spotify original so it's not available anywhere else.
When I start listening to the latest episode on my phone, the episode starts immediately with the hosts talking, and the length is 46:40. But when I use Spotify Connect to play on my Sonos One, the podcast starts with an advert, and the length changes to 49:14.
It's like Spotify is ignoring my premium subscription when it plays on my Sonos, although I haven't noticed this behaviour on any music or any other Spotify original podcasts. I checked and I'm definitely signed into the same account on both my phone and my Sonos system.