Hey, thanks for the report. Could you try disabling completion sound, restarting Cursor, and then enabling it again? Also, start a new chat. Additionally, check the sound settings and see if the Task completed sound is enabled.
In addition to last message, I saw only notifications WITHOUT a sound, until I run smth from here : ctrl + shift + P : maybe need to select Refresh composer, or other options (but it has no visual effect) → after that I at last started to hear that ■■■■■■■ sound