When casting music to chromecast-enabled devices, I have noticed that music will sometimes pause for a few seconds (anwhere from 1-15 seconds) before resuming. When the pause happens, the Spotify app will continue moving the playback bar and the time remaining on the song will decrease even though no audio is played. Once it resumes playing the Spotify app will skip back to show it's accurate playback location. Music will always resume automatically on its own from the same place it left off.
This appears to happen regardless of which chromecast device I stream to and has happened when streaming to any one individual device listed above as well as when streaming to Google speaker groups that comprise of any of the above devices. When streaming to speaker groups, all speakers will stop playing at the same time and will resume at the same time as well. As such, it appears that all devices are in perfect sync.
The issue happens intermittently and without any type of consistency. Sometimes it will work perfectly for a few hours, sometimes it has the pauses multiple times within one hour.
I have tried rebooting my router/modem, resetting my router/modem to factory settings, and have also tried streaming music from Google Play Music to these same devices without issue. This issue happens when I use Google Assistant on a Google Home Mini to start playing the music, when I use the iOS app, the web player (in Chrome so I can cast) or using the Android app.
While the Sony soundbar supports Spotify Connect, I typically use Google Assistant to start music so it plays through the built-in Chromecast. I have not done testing to see if the issue occurs while usign Spotify Connect. I can confirm that I have no issues when listening directly on my phone or computer.
I have AT&T gigabit fiber internet and the Sony soudbar is hardwired directly to the router. All devices are within 13 feet of the router, as I am in a rather small apartment. During this time that pausing happens, I do not appear to be having any internet issues as pings from my computer to outside IP addresses continue to be responded to without issue. I actually setup a continuous ping to Google's server for a few days and didn't have any dropped responeses even though I encountered these pauses during that time.
I searched through the community but could only find information regarding a similar issue that was to be resolved by updating or reinstalling the Spotify app, however there is no way to do so on the Google Home devices as Google manages the firmware on these devices.