Saw this again on Sept 17th. Only once (as far as I know). No repro steps, but I wanted to open a ticket to at least investigate. Feel free to ping me if you need any more details.
Summary of what happened:
1. I opened my computer from sleep around 20:34 local time (could have been a minute or two earlier, but that's the first page view I see in Chrome history)
2. At 20:34 a reply was posted to my message to a public channel (Plugins Marketplace) in the Contributors team.
3. At 20:35, a second reply was posted
Observed: Neither triggered a mention, even though Reply Notifications in "Account Settings > Notifications" are set to "Trigger notifications on messages in reply threads that I start or participate in".
My status was set to Do Not Disturb (DND) at the time
I see the attached JS error in the console. Seems this may have occurred around the time I woke computer from sleep
Since my status was DND, no desktop/email/push notification was triggered