Welcome to Roon. Unfortunately, I am just a user and don’t have any Sonos. However, at least I found two older posts suggesting that this seems to be a common issue with Sonos and Roon. In the first thread, crossfade was enabled, in the second it was not. Possibly these are different issues
Maybe a fellow user with Sonos experience can add something, else I’m afraid you have to wait for Roon support to help