A
Is the connection dropping? Are you sure no control buttons were pressed? Does it disconnect you or just stop playing content? When it stops, is there any other content playing on your phone (some ads will play videos, which will override music apps' audio output)? A notification came through (although in this case, audio should lower and then come back to the original level after the notification)?
Welcome to Android Central! Which phone do you have? Are you saying that when you're using any Bluetooth device to listen to music on your phone, it inevitably pauses on its own? Is the app that's playing the media still in the foreground, or has it closed?
Chromecast works via wi-fi, not Bluetooth, so that wouldn't be a Bluetooth issue. Smart speakers aren't necessarily a Bluetooth issue either, but that depends on which smart speaker you're using.
Does the playback stop only when the phone's screen has gone to sleep?
Any power-saving modes turned on, or 3rd party battery-saver/"RAM-booster" apps installed?
See if this also happens in Safe Mode: https://forums.androidcentral.com/e...estart-phone-in-safe-mode.html&token=XuSCJDEu. You'll only be able to test preinstalled apps, but YouTube should be one of them.
One more thing to try -- uninstall all updates to Chrome, in case a recent update is causing issues. Chrome handles Android System Webview on Nougat or higher, and sometimes these updates can cause issues with specific phones.
Try temporarily turning off wi-fi (if feasible), since sometimes 2.4 GHz wi-fi can interfere with Bluetooth signal (since BT also uses 2.4 GHz). Or, if you have 5 GHz wi-fi available, use that.
The fact that it works in Safe Mode implies that something you installed is causing the problem. If you've uninstalled every 3rd party app and it still happens, then the next step would be a factory reset without automatically restoring the phone to its previous state (so that apps don't automatically reinstall), and then installing apps one by one, checking after each install to see if the Bluetooth problem returns.