In notification-related documentation, we can find that Collaborator does not send repeated notifications:
When Collaborator Does Not Send Notifications
Collaborator does not send repeated notifications. If several events occur within the review, then only the notification of the first event is sent. After which, the notification recipients have their state set to "Active". They will not receive further notifications, except for phase change notifications.
For some type of messages (eg. chat responses) this behavior leads to missed messages and increasing of review time. As a workaround, we may use the "Poke" feature, but it has some drawbacks: I may forget to poke and I have to explain to every review member about this behavior.
Allowing sending repeated notifications (perhaps via per-notify configuration) should solve this problem