Hey! Sounds frustrating — especially since everything else is working fine. In Opera, this often happens because of a sound or site permission issue. Try clicking the lock icon next to the Spotify web address and make sure “Sound” is set to Allow. Also, check Opera’s site settings under Settings → Privacy and Security → Site Settings → Sound to confirm Spotify isn’t muted.
If that doesn’t help, clear cookies and cache for Spotify, then restart the browser. Sometimes hardware acceleration can also cause audio bugs — try turning it off under Settings → System. After that, reload Spotify and test again — it usually fixes the no-sound issue.
If none of these steps help, and since you mentioned the issue is still happening, you can check the discussion here for more details https://community.spotify.com/t5/Accounts/I-got-randomly-logged-out-of-my-spotify-premium-account-and-it-says-it/td-p/6399398
You could also try the Spotify desk top app, which usually handles playback more reliably than browsers.