When I start a song from Spotify on my phone it takes a good 40 seconds before it will start on Chromecast. When it goes to the next song on the playlist it again pauses for about 40 seconds. On the phone I can see the progress bar moving in the Spotify app but no music plays from Chromecast. Then suddenly the progress bar will go back to the beginning and the music starts. My WiFi is solid as is my download speed of 60 Mbps. Using android on my phone but it does the same with iPhones in the household too. Happens with other Google cast devices as well ie Google home hub. All apps and op systems are up-to-date as is Chromecast firmware.
It's like the Chromecast is buffering or not able to pull the song from the cloud instantly.