This has been classified as a minor bug and added to our pipeline for next week. A workaround has been shared with affected users.

We’re currently aware of an issue where some notifications are not being delivered. In our internal tests, we noticed that when a client sends a message in the chat without tagging (@mentioning) anyone, only the designer assigned to the request receives the notification. There have also been reports of cases where customers may not be receiving notifications of comments made without tagging.