I occasionally, although not frequently, use PocketCasts on my Sonos, without any issues.
It seems odd that none of these systems can ‘see’ the respective servers to get data from them suggests a network issue with your Sonos system. I’d be looking for any sort of port blocking options, such as VPNs, work profiles, firewalls, or even virus protection. Failing that, I would call Sonos Support directly to discuss it.
When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.
