OutlookMailboxCtpMonitor unhealthy on one of our Exchange 2013 server

We have 3 Exchange 2013 in a DAG configuration behind a Kemp Loadbalancer. One of the server is giving us an error message in SCOM that Outlook is unhealthy. When we run the Get-ServerHealth command we get that the message that OutlookMailboxCtpMonitor and OutlookArchiveCtpMonitor are unhealthy. What does that the mean ?

It'a big problem for us because rpc over http doesn't seem to work on that server so we had to disable it in the Kemp Loadbalancer.

Thanks,

Antonio