Without more data, it’s really hard to tell.
There are multiple threads about issues with Spotify, including one I just read about a thread outside of Sonos that is suggesting that Spotify themselves are having issues.
We do mostly know that if your music on other streams is working fine, then the issue is not in your Sonos, and somewhere upstream of your router, either in DNS land, or in the Spotify server that your speakers are attempting to connect to.
However, there’s a actually still a small possibility that we’re looking at a potential of wifi interference, since each streamer has differing tolerances for “disconnects”. But given the many other threads, my bet would be on it being a Spotify issue. However, that shouldn’t stop you from reading the linked FAQ, one never knows.