If you look at the event log section, it tells you exactly what the issue is:
Could not update system with IPAddress x.x.x.x and name xxx. No contact with system.
It means TMS couldn't update the phone book that is assigned to that endpoint because it could be offline or TMS is using an old IP address when it tries to communicated to it.
The message saying "Some, but not all systems updated" means that TMS was able to update the phone books on other endpoints without issue.
