Now that legacy TuneIn is gone from the new (buggy) iOS controller and all my custom radio stations (in my case from Digitally Imported di.fm) were gone and there is no information on the Sonos site I luckily found a way to get them back. However it involves recreating them which can be labour intensive depending on how many you have. You will also need the IOS version of TuneIn for this to work. No premium sign up required.
Here are the instructions from TuneIn https://help.tunein.com/en/support/solutions/articles/151000172377-what-is-a-custom-url-and-how-can-i-add-it-to-sonos-
The Custom URL feature allows you to listen to a private streaming URL, most likely not in the TuneIn directory, using the TuneIn and Sonos app.
To add a custom URL to your Sonos:
- Ensure that TuneIn (new) is added on your Sonos app
- Log into the iOS or Android TuneIn app using the same TuneIn credentials you use on Sonos
- On the TuneIn app, navigate to Library
- Tap on customURL and enter the desired stream URL
- While listening to that stream, tap the favorite (heart) icon on the now playing screen
- Select “favorite station”
- Enter a name for the custom stream
- Return to TuneIn (new) on your Sonos app, and you should now see that station in your favorites gallery there.
So far this works fine on my system.