The push notifications from PubNub seem to not get processed in most cases. If the two users restart their clients and have a fresh start with no network issues, the PubNub notifications go through. However, once you introduce a poor network condition (unplug the network for a second or introduce high enough of latency to reach 500ms or more), even after the poor network condition is removed, most pubnub push notifications are missed until it resorts to the 4 minute poll to get the update.

Restart of the editor, refresh the history window, or waiting up to 4 minutes gets around the issue for that one publish/update, but then the bug process begins anew. In-progress notifications are also affected but are on a different timer which might be longer than the 4 minute timer.

Issue seems to only affect the 2017.2 branch and later.