>>It does sometimes work and then stops working again. I think it works after re-start, then stops working. All other applications work fine for the sound. E.g. I can play video on Facebook and hear sound.
>
>Would you be able to remember if this should have been only a notification for a reply, or a private message and agent? Also, can you let me know into which browser this applies?

I am using Google Chrome Version 57.0.2987.133

I didn't get any notification about your reply. I think it applies to everything when it's not working.

I'll try closing this tab and re-opening LE. Try to reply in ~10 min.

UPDATE. I closed LE tab and re-opened the site. Someone please reply to this message to test the sound.